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>
