[huangji6693-max]

Summary

Fixes four file and event consistency defects reported in #149:

1. Reject conflicting /files/delete selectors (routes/files/delete.ts): Reject requests supplying both file_id and file_path with HTTP 400 (Provide only one of file_id or file_path) before mutating state so a single request cannot delete two distinct files while emitting only one event.
2. Reject empty / root file paths on upsert and rename (routes/files/upsert.ts, routes/files/rename.ts): Validate normalizePath(body.file_path) and normalizePath(body.new_file_path) and return HTTP 400 if empty ("" or "/").
3. Compare parsed timestamps in listEvents({ since }) (lib/db/db-client.ts): Use Date.parse(e.created_at) > Date.parse(since) rather than lexicographical string comparison so ISO timestamps with timezone offsets are ordered by instant.
4. Avoid mutating previous events array snapshots in renameFile (lib/db/db-client.ts): Construct a new events: [...state.events, createdEvent, deletedEvent] array instead of mutating state.events in place.

Closes #149
Fixes #149
/claim #149

Verification

• bun test tests/rename-events.test.ts tests/routes/empty-file-path.test.ts tests/routes/event-timestamp.test.ts tests/routes/selector-conflict.test.ts (4 pass, 0 fail)
• bunx tsc --noEmit
• bun run format:check

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