Move schema_migrations table creation into 000.sql with INTEGER version column

Replace the monolithic schema.sql embed with a numbered migration system
following the pixa pattern:

- Add schema/000.sql: bootstrap migration creating schema_migrations table
  with INTEGER PRIMARY KEY version column and applied_at timestamp
- Move full schema to schema/001.sql (renamed from schema.sql)
- Remove redundant schema/008_uploads.sql (uploads table already in main schema)
- Rewrite database.go migration logic:
  - Embed schema/*.sql directory instead of single schema.sql
  - bootstrapMigrationsTable() checks for table existence, applies 000.sql
  - applyMigrations() iterates numbered files, skips already-applied versions
  - ParseMigrationVersion() extracts version from filenames (e.g. 001.sql)
  - Go code does zero INSERTs for bootstrap — 000.sql is self-contained
- Update database_test.go to verify schema_migrations table exists

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);