feat(sqlite): initial stable release v0.9.0

Pure-Go CGO-free SQLite client with launcher lifecycle, write-mutex serialisation, health check, unit-of-work via context injection, and structured error mapping.

What's included:
- Executor / Tx / Client / Component interfaces using database/sql native types
- Tx.Commit() / Tx.Rollback() without ctx, matching the honest database/sql contract
- New(logger, cfg) constructor; database opened in OnInit
- Config struct with env-tag support; default Pragmas: WAL + 5s busy timeout + FK enforcement
- PRAGMA foreign_keys = ON enforced explicitly in OnInit
- writeMu sync.Mutex acquired by UnitOfWork.Do to serialise writes and prevent SQLITE_BUSY
- UnitOfWork via context injection; GetExecutor(ctx) returns active Tx or *sql.DB
- HandleError mapping SQLite extended error codes to xerrors codes (unique/primary-key → AlreadyExists, foreign-key → InvalidInput, ErrNoRows → NotFound)
- health.Checkable at LevelCritical; pure-Go modernc.org/sqlite driver (CGO_ENABLED=0 compatible)

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

docs/adr/ADR-001-modernc-pure-go-driver.md

@@ -0,0 +1,43 @@
+# ADR-001: Pure-Go SQLite Driver via modernc.org/sqlite
+
+**Status:** Accepted
+**Date:** 2026-03-18
+
+## Context
+
+SQLite requires a C library on the host system. The standard `mattn/go-sqlite3` driver wraps the
+C library via cgo. This means:
+
+- CGO must be enabled at build time (`CGO_ENABLED=1`).
+- A C toolchain must be present in every build and CI environment.
+- Cross-compilation is significantly harder (requires a cross-compiling C toolchain).
+- Static binaries are complicated to produce without additional linker flags.
+
+For a micro-lib that should work in minimal container environments and cross-compile without
+ceremony, this is a poor baseline.
+
+## Decision
+
+Use `modernc.org/sqlite` as the SQLite driver. This is a transpilation of the official SQLite
+amalgamation from C to Go, producing a pure-Go implementation with no CGO dependency. It is
+registered under the driver name `"sqlite"` and is otherwise compatible with `database/sql`.
+
+The import is a blank import in `sqlite.go`:
+
+```go
+import _ "modernc.org/sqlite" // register sqlite driver
+```
+
+## Consequences
+
+**Positive:**
+- `CGO_ENABLED=0` builds work out of the box.
+- Cross-compilation requires no special toolchain setup.
+- CI environments need only the Go toolchain.
+- Minimal container images (scratch, distroless) are straightforward targets.
+
+**Negative:**
+- `modernc.org/sqlite` lags slightly behind the official SQLite release cadence.
+- Transpiled code is harder to debug at the C level than `mattn/go-sqlite3`.
+- The driver name is `"sqlite"` not `"sqlite3"`, which would conflict with any project that
+  also imports `mattn/go-sqlite3`.