refactor(store): swap mattn/go-sqlite3 for modernc.org/sqlite

Pure-Go SQLite driver — no CGO, no C compiler. Enables:
- static binaries (verified: `file` shows statically linked)
- cross-compile to linux/arm64, darwin/amd64+arm64, windows/amd64+arm64
- goreleaser now builds 6 OS/arch targets + windows .zip
- Dockerfile drops gcc/musl-dev, sets CGO_ENABLED=0
- release-binaries drops gcc/musl-dev

Driver name changes sqlite3 → sqlite, DSN pragmas use
_pragma=name(value) format. All tests pass CGO=0 and CGO=1 -race.

Homebrew cask block removed (was skip_upload:true dead config).

internal/store/sqlite.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"log"
 
-	_ "github.com/mattn/go-sqlite3"
+	_ "modernc.org/sqlite"
 )
 
 type SQLiteDialect struct{}
@@ -19,16 +19,16 @@ func NewSQLiteStore(path string) (*SQLStore, error) {
 	// these pragmas are no-ops or harmful for the in-memory test DB.)
 	dsn := path
 	if path != ":memory:" {
-		dsn = fmt.Sprintf("file:%s?_journal_mode=WAL&_busy_timeout=5000&_synchronous=NORMAL", path)
+		dsn = fmt.Sprintf("file:%s?_pragma=journal_mode(wal)&_pragma=busy_timeout(5000)&_pragma=synchronous(normal)", path)
 	}
-	s, err := NewSQLStore("sqlite3", dsn, &SQLiteDialect{})
+	s, err := NewSQLStore("sqlite", dsn, &SQLiteDialect{})
 	if err != nil {
 		return nil, err
 	}
 	return s, nil
 }
 
-func (d *SQLiteDialect) DriverName() string { return "sqlite3" }
+func (d *SQLiteDialect) DriverName() string { return "sqlite" }
 func (d *SQLiteDialect) BoolFalse() string  { return "0" }
 
 func (d *SQLiteDialect) CreateTablesSQL() []string {