feat: move schema_migrations into 000_bootstrap.sql (#95)

## Summary

- Moves schema_migrations table creation from inline Go code into internal/db/schema/000_bootstrap.sql
- Bootstrap SQL is executed directly before the migration loop (which starts from 001+)
- Go code does zero INSERTs for the bootstrap — 000_bootstrap.sql handles the INSERT OR IGNORE for version 0
- loadMigrations() skips 000.sql so it is not processed by the normal migration loop

Follows the sneak/pixa pattern.

closes #91

## Test plan

- [x] All existing tests pass (make test in Docker)
- [x] Linter passes (make lint)
- [x] Docker build succeeds (docker build --no-cache .)
- [x] Existing databases with schema_migrations table work (CREATE TABLE IF NOT EXISTS + INSERT OR IGNORE are idempotent)

Generated with Claude Code

Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: sneak/chat#95
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
Co-committed-by: clawbot <sneak+clawbot@sneak.cloud>

internal/db/db.go

@@ -135,13 +135,21 @@ type migration struct {
 func (database *Database) runMigrations(
 	ctx context.Context,
 ) error {
-	_, err := database.conn.ExecContext(ctx,
-		`CREATE TABLE IF NOT EXISTS schema_migrations (
-		 version INTEGER PRIMARY KEY,
-		 applied_at DATETIME DEFAULT CURRENT_TIMESTAMP)`)
+	bootstrap, err := SchemaFiles.ReadFile(
+		"schema/000.sql",
+	)
 	if err != nil {
 		return fmt.Errorf(
-			"create schema_migrations: %w", err,
+			"read bootstrap migration: %w", err,
+		)
+	}
+
+	_, err = database.conn.ExecContext(
+		ctx, string(bootstrap),
+	)
+	if err != nil {
+		return fmt.Errorf(
+			"execute bootstrap migration: %w", err,
 		)
 	}
 
@@ -270,6 +278,11 @@ func (database *Database) loadMigrations() (
 			continue
 		}
 
+		// Skip bootstrap migration; it is executed separately.
+		if version == 0 {
+			continue
+		}
+
 		content, readErr := SchemaFiles.ReadFile(
 			"schema/" + entry.Name(),
 		)

internal/db/schema/000.sql

@@ -0,0 +1,6 @@
+-- Bootstrap: create the schema_migrations table itself.
+CREATE TABLE IF NOT EXISTS schema_migrations (
+    version INTEGER PRIMARY KEY,
+    applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+INSERT OR IGNORE INTO schema_migrations (version) VALUES (0);