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/database_test.go

@@ -2,6 +2,7 @@ package database
 
 import (
 	"context"
+	"database/sql"
 	"fmt"
 	"path/filepath"
 	"testing"
@@ -26,9 +27,10 @@ func TestDatabase(t *testing.T) {
 		t.Fatal("database connection is nil")
 	}
 
-	// Test schema creation (already done in New)
+	// Test schema creation (already done in New via migrations)
 	// Verify tables exist
 	tables := []string{
+		"schema_migrations",
 		"files", "file_chunks", "chunks", "blobs",
 		"blob_chunks", "chunk_files", "snapshots",
 	}
@@ -99,3 +101,139 @@ func TestDatabaseConcurrentAccess(t *testing.T) {
 		t.Errorf("expected 10 chunks, got %d", count)
 	}
 }
+
+func TestParseMigrationVersion(t *testing.T) {
+	tests := []struct {
+		name      string
+		filename  string
+		wantVer   int
+		wantError bool
+	}{
+		{name: "valid 000.sql", filename: "000.sql", wantVer: 0, wantError: false},
+		{name: "valid 001.sql", filename: "001.sql", wantVer: 1, wantError: false},
+		{name: "valid 099.sql", filename: "099.sql", wantVer: 99, wantError: false},
+		{name: "valid with description", filename: "001_initial_schema.sql", wantVer: 1, wantError: false},
+		{name: "valid large version", filename: "123_big_migration.sql", wantVer: 123, wantError: false},
+		{name: "invalid alpha version", filename: "abc.sql", wantVer: 0, wantError: true},
+		{name: "invalid mixed chars", filename: "12a.sql", wantVer: 0, wantError: true},
+		{name: "invalid no extension", filename: "schema.sql", wantVer: 0, wantError: true},
+		{name: "empty string", filename: "", wantVer: 0, wantError: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := ParseMigrationVersion(tc.filename)
+			if tc.wantError {
+				if err == nil {
+					t.Errorf("ParseMigrationVersion(%q) = %d, nil; want error", tc.filename, got)
+				}
+				return
+			}
+			if err != nil {
+				t.Errorf("ParseMigrationVersion(%q) unexpected error: %v", tc.filename, err)
+				return
+			}
+			if got != tc.wantVer {
+				t.Errorf("ParseMigrationVersion(%q) = %d; want %d", tc.filename, got, tc.wantVer)
+			}
+		})
+	}
+}
+
+func TestApplyMigrations_Idempotent(t *testing.T) {
+	ctx := context.Background()
+
+	conn, err := sql.Open("sqlite", ":memory:?_foreign_keys=ON")
+	if err != nil {
+		t.Fatalf("failed to open database: %v", err)
+	}
+	defer func() {
+		if err := conn.Close(); err != nil {
+			t.Errorf("failed to close database: %v", err)
+		}
+	}()
+
+	conn.SetMaxOpenConns(1)
+	conn.SetMaxIdleConns(1)
+
+	// First run: apply all migrations.
+	if err := applyMigrations(ctx, conn); err != nil {
+		t.Fatalf("first applyMigrations failed: %v", err)
+	}
+
+	// Count rows in schema_migrations after first run.
+	var countBefore int
+	if err := conn.QueryRowContext(ctx, "SELECT COUNT(*) FROM schema_migrations").Scan(&countBefore); err != nil {
+		t.Fatalf("failed to count schema_migrations after first run: %v", err)
+	}
+
+	// Second run: must be a no-op.
+	if err := applyMigrations(ctx, conn); err != nil {
+		t.Fatalf("second applyMigrations failed: %v", err)
+	}
+
+	// Count rows in schema_migrations after second run — must be unchanged.
+	var countAfter int
+	if err := conn.QueryRowContext(ctx, "SELECT COUNT(*) FROM schema_migrations").Scan(&countAfter); err != nil {
+		t.Fatalf("failed to count schema_migrations after second run: %v", err)
+	}
+
+	if countBefore != countAfter {
+		t.Errorf("schema_migrations row count changed: before=%d, after=%d", countBefore, countAfter)
+	}
+}
+
+func TestBootstrapMigrationsTable_FreshDatabase(t *testing.T) {
+	ctx := context.Background()
+
+	conn, err := sql.Open("sqlite", ":memory:?_foreign_keys=ON")
+	if err != nil {
+		t.Fatalf("failed to open database: %v", err)
+	}
+	defer func() {
+		if err := conn.Close(); err != nil {
+			t.Errorf("failed to close database: %v", err)
+		}
+	}()
+
+	conn.SetMaxOpenConns(1)
+	conn.SetMaxIdleConns(1)
+
+	// Verify schema_migrations does NOT exist yet.
+	var tableBefore int
+	if err := conn.QueryRowContext(ctx,
+		"SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name='schema_migrations'",
+	).Scan(&tableBefore); err != nil {
+		t.Fatalf("failed to check for table before bootstrap: %v", err)
+	}
+	if tableBefore != 0 {
+		t.Fatal("schema_migrations table should not exist before bootstrap")
+	}
+
+	// Run bootstrap.
+	if err := bootstrapMigrationsTable(ctx, conn); err != nil {
+		t.Fatalf("bootstrapMigrationsTable failed: %v", err)
+	}
+
+	// Verify schema_migrations now exists.
+	var tableAfter int
+	if err := conn.QueryRowContext(ctx,
+		"SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name='schema_migrations'",
+	).Scan(&tableAfter); err != nil {
+		t.Fatalf("failed to check for table after bootstrap: %v", err)
+	}
+	if tableAfter != 1 {
+		t.Fatalf("schema_migrations table should exist after bootstrap, got count=%d", tableAfter)
+	}
+
+	// Verify version 0 row exists.
+	var version int
+	if err := conn.QueryRowContext(ctx,
+		"SELECT version FROM schema_migrations WHERE version = 0",
+	).Scan(&version); err != nil {
+		t.Fatalf("version 0 row not found in schema_migrations: %v", err)
+	}
+	if version != 0 {
+		t.Errorf("expected version 0, got %d", version)
+	}
+}