Move schema_migrations table creation into 000.sql with INTEGER version column (#58)

Closes #57

Adopts the [pixa migration pattern](sneak/pixa#36) for schema management. Replaces the monolithic `schema.sql` embed with a numbered migration system.

## Changes

### New: `schema/000.sql` — Bootstrap migration
- Creates `schema_migrations` table with `INTEGER PRIMARY KEY` version column
- Self-contained: includes both `CREATE TABLE IF NOT EXISTS` and `INSERT OR IGNORE` for version 0
- Go code does zero INSERTs for bootstrap — just reads and executes 000.sql

### Renamed: `schema.sql` → `schema/001.sql` — Initial schema migration
- Full Vaultik schema (files, chunks, blobs, snapshots, uploads, all indexes)
- Updated header comment to identify it as migration 001

### Removed: `schema/008_uploads.sql`
- Redundant — the uploads table with its current schema was already in the main schema file
- The 008 file had a stale/different schema (TIMESTAMP instead of INTEGER, missing snapshot_id FK)

### Rewritten: `database.go` — Migration engine
- `//go:embed schema/*.sql` replaces `//go:embed schema.sql`
- `bootstrapMigrationsTable()`: checks if `schema_migrations` table exists, applies 000.sql if missing
- `applyMigrations()`: iterates through numbered .sql files, checks `schema_migrations` for each version, applies and records pending ones
- `collectMigrations()`: reads embedded schema dir, returns sorted filenames
- `ParseMigrationVersion()`: extracts numeric version from filenames like `001.sql` or `001_description.sql` (exported for testing)
- Old `createSchema()` removed entirely

### Updated: `database_test.go`
- Verifies `schema_migrations` table exists alongside other core tables

## Verification

`docker build .` passes — formatting, linting, all tests green.

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #58
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/database/schema/000.sql

@@ -0,0 +1,9 @@
+-- Migration 000: Schema migrations tracking table
+-- Applied as a bootstrap step before the normal migration loop.
+
+CREATE TABLE IF NOT EXISTS schema_migrations (
+    version INTEGER PRIMARY KEY,
+    applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+
+INSERT OR IGNORE INTO schema_migrations (version) VALUES (0);

internal/database/schema/001.sql

@@ -0,0 +1,135 @@
+-- Migration 001: Initial Vaultik schema
+-- All core tables for tracking files, chunks, blobs, snapshots, and uploads.
+
+-- Files table: stores metadata about files in the filesystem
+CREATE TABLE IF NOT EXISTS files (
+    id TEXT PRIMARY KEY,  -- UUID
+    path TEXT NOT NULL UNIQUE,
+    source_path TEXT NOT NULL DEFAULT '',  -- The source directory this file came from (for restore path stripping)
+    mtime INTEGER NOT NULL,
+    size INTEGER NOT NULL,
+    mode INTEGER NOT NULL,
+    uid INTEGER NOT NULL,
+    gid INTEGER NOT NULL,
+    link_target TEXT
+);
+
+-- Create index on path for efficient lookups
+CREATE INDEX IF NOT EXISTS idx_files_path ON files(path);
+
+-- File chunks table: maps files to their constituent chunks
+CREATE TABLE IF NOT EXISTS file_chunks (
+    file_id TEXT NOT NULL,
+    idx INTEGER NOT NULL,
+    chunk_hash TEXT NOT NULL,
+    PRIMARY KEY (file_id, idx),
+    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE,
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash)
+);
+
+-- Index for efficient chunk lookups (used in orphan detection)
+CREATE INDEX IF NOT EXISTS idx_file_chunks_chunk_hash ON file_chunks(chunk_hash);
+
+-- Chunks table: stores unique content-defined chunks
+CREATE TABLE IF NOT EXISTS chunks (
+    chunk_hash TEXT PRIMARY KEY,
+    size INTEGER NOT NULL
+);
+
+-- Blobs table: stores packed, compressed, and encrypted blob information
+CREATE TABLE IF NOT EXISTS blobs (
+    id TEXT PRIMARY KEY,
+    blob_hash TEXT UNIQUE,
+    created_ts INTEGER NOT NULL,
+    finished_ts INTEGER,
+    uncompressed_size INTEGER NOT NULL DEFAULT 0,
+    compressed_size INTEGER NOT NULL DEFAULT 0,
+    uploaded_ts INTEGER
+);
+
+-- Blob chunks table: maps chunks to the blobs that contain them
+CREATE TABLE IF NOT EXISTS blob_chunks (
+    blob_id TEXT NOT NULL,
+    chunk_hash TEXT NOT NULL,
+    offset INTEGER NOT NULL,
+    length INTEGER NOT NULL,
+    PRIMARY KEY (blob_id, chunk_hash),
+    FOREIGN KEY (blob_id) REFERENCES blobs(id) ON DELETE CASCADE,
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash)
+);
+
+-- Index for efficient chunk lookups (used in orphan detection)
+CREATE INDEX IF NOT EXISTS idx_blob_chunks_chunk_hash ON blob_chunks(chunk_hash);
+
+-- Chunk files table: reverse mapping of chunks to files
+CREATE TABLE IF NOT EXISTS chunk_files (
+    chunk_hash TEXT NOT NULL,
+    file_id TEXT NOT NULL,
+    file_offset INTEGER NOT NULL,
+    length INTEGER NOT NULL,
+    PRIMARY KEY (chunk_hash, file_id),
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash),
+    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
+);
+
+-- Index for efficient file lookups (used in orphan detection)
+CREATE INDEX IF NOT EXISTS idx_chunk_files_file_id ON chunk_files(file_id);
+
+-- Snapshots table: tracks backup snapshots
+CREATE TABLE IF NOT EXISTS snapshots (
+    id TEXT PRIMARY KEY,
+    hostname TEXT NOT NULL,
+    vaultik_version TEXT NOT NULL,
+    vaultik_git_revision TEXT NOT NULL,
+    started_at INTEGER NOT NULL,
+    completed_at INTEGER,
+    file_count INTEGER NOT NULL DEFAULT 0,
+    chunk_count INTEGER NOT NULL DEFAULT 0,
+    blob_count INTEGER NOT NULL DEFAULT 0,
+    total_size INTEGER NOT NULL DEFAULT 0,
+    blob_size INTEGER NOT NULL DEFAULT 0,
+    blob_uncompressed_size INTEGER NOT NULL DEFAULT 0,
+    compression_ratio REAL NOT NULL DEFAULT 1.0,
+    compression_level INTEGER NOT NULL DEFAULT 3,
+    upload_bytes INTEGER NOT NULL DEFAULT 0,
+    upload_duration_ms INTEGER NOT NULL DEFAULT 0
+);
+
+-- Snapshot files table: maps snapshots to files
+CREATE TABLE IF NOT EXISTS snapshot_files (
+    snapshot_id TEXT NOT NULL,
+    file_id TEXT NOT NULL,
+    PRIMARY KEY (snapshot_id, file_id),
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
+    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
+);
+
+-- Index for efficient file lookups (used in orphan detection)
+CREATE INDEX IF NOT EXISTS idx_snapshot_files_file_id ON snapshot_files(file_id);
+
+-- Snapshot blobs table: maps snapshots to blobs
+CREATE TABLE IF NOT EXISTS snapshot_blobs (
+    snapshot_id TEXT NOT NULL,
+    blob_id TEXT NOT NULL,
+    blob_hash TEXT NOT NULL,
+    PRIMARY KEY (snapshot_id, blob_id),
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
+    FOREIGN KEY (blob_id) REFERENCES blobs(id) ON DELETE CASCADE
+);
+
+-- Index for efficient blob lookups (used in orphan detection)
+CREATE INDEX IF NOT EXISTS idx_snapshot_blobs_blob_id ON snapshot_blobs(blob_id);
+
+-- Uploads table: tracks blob upload metrics
+CREATE TABLE IF NOT EXISTS uploads (
+    blob_hash TEXT PRIMARY KEY,
+    snapshot_id TEXT NOT NULL,
+    uploaded_at INTEGER NOT NULL,
+    size INTEGER NOT NULL,
+    duration_ms INTEGER NOT NULL,
+    FOREIGN KEY (blob_hash) REFERENCES blobs(blob_hash),
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE
+);
+
+-- Index for efficient snapshot lookups
+CREATE INDEX IF NOT EXISTS idx_uploads_snapshot_id ON uploads(snapshot_id);

internal/database/schema/008_uploads.sql

@@ -1,11 +0,0 @@
--- Track blob upload metrics
-CREATE TABLE IF NOT EXISTS uploads (
-    blob_hash TEXT PRIMARY KEY,
-    uploaded_at TIMESTAMP NOT NULL,
-    size INTEGER NOT NULL,
-    duration_ms INTEGER NOT NULL,
-    FOREIGN KEY (blob_hash) REFERENCES blobs(blob_hash)
-);
-
-CREATE INDEX idx_uploads_uploaded_at ON uploads(uploaded_at);
-CREATE INDEX idx_uploads_duration ON uploads(duration_ms);