Closes#28
Migration filenames now follow the pattern `<version>_<description>.sql` (e.g. `001_initial_schema.sql`). The version stored in `schema_migrations` is the numeric prefix only, not the full filename stem.
## Changes
- **`ParseMigrationVersion()`** — new exported function that extracts the numeric prefix from migration filenames. Validates that the prefix is purely numeric and rejects malformed filenames (empty prefix, non-numeric characters, leading underscore).
- **Renamed `001.sql` → `001_initial_schema.sql`** — migration files can now have descriptive names while the tracked version remains `001`. This is safe pre-1.0.0 (no installed base).
- **Deduplicated migration logic** — `runMigrations()` and `ApplyMigrations()` now share a single `applyMigrations()` implementation, plus extracted `collectMigrations()` and `ensureMigrationsTable()` helpers.
- **Unit tests** — `TestParseMigrationVersion` covers valid patterns (version-only, with description, multi-digit, multiple underscores) and error cases (empty, leading underscore, non-numeric, mixed alphanumeric). `TestApplyMigrations` and `TestApplyMigrationsIdempotent` verify end-to-end migration application against an in-memory SQLite database.
Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #33
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
Migrations are stored in schema/*.sql and embedded via go:embed.
Applied migrations are tracked in schema_migrations table.
Initial schema includes source_content, source_metadata, output_content,
request_cache, negative_cache, and cache_stats tables.
