fix(core): address PR review — buffer ordering, flush safety, dbPath in logs

- Flush buffer before appendAgentLogBatch to prevent rowid ordering
  inversion when callers interleave buffered and direct writes (P1)
- Wrap size-triggered flush in try-catch for consistency with timer path
- Move bumpLastModified inside transactions for atomicity
- Expose db.path getter and include DB path in all flush error logs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/core/src/db.ts

@@ -698,6 +698,8 @@ export class Database {
   private db: DatabaseSync;
   private readonly dbPath: string;
   private readonly inMemory: boolean;
+  /** Returns the database file path (or ":memory:" for in-memory databases). */
+  get path(): string { return this.dbPath; }
   corruptionDetected = false;
   /** Tracks transaction nesting depth for savepoint-based nested transactions. */
   private transactionDepth = 0;