fix: graceful error handling for /undo

[wjiuxing]

Summary

Fixes clopca#17 — error logs appearing after /undo in opencode.

Root Cause

open-mem's hooks assume "write = permanent" with no undo/cleanup path. After /undo, opencode deletes messages but continues triggering hooks (e.g. session.idle), causing open-mem to error when referencing deleted data.

Changes

Logger utility (src/utils/logger.ts)

• New Logger class with level-gated output (debug → console.log, warn → console.warn, error → console.error)
• Configurable via OPEN_MEM_LOG_LEVEL env var (default: warn)

Error handling (all hooks)

• Replace console.error with Logger instance — errors now properly categorized
• Hooks no longer crash on missing/deleted data — gracefully degrade

Cleanup mechanism (src/db/pending.ts)

• Add deleteBySessionId() to PendingMessageRepository — removes pending/failed messages for a session
• Wired into session lifecycle cleanup path

Tests (970 pass, 0 fail)

• Logger test suite: 121 lines covering all levels, routing, and configuration
• deleteBySessionId tests: 3 tests covering status filtering, cross-session isolation
• Updated all hook tests to pass Logger parameter (now required)

Files Changed (18 files, +451/-34)

Area	Files	What
Core	src/utils/logger.ts	New Logger utility
Core	src/db/pending.ts	deleteBySessionId method
Hooks	chat-capture.ts, compaction.ts, context-inject.ts, session-events.ts, tool-capture.ts	Replace console.error with Logger
Wiring	src/index.ts, src/platform-worker.ts, src/adapters/platform/runtime.ts	Logger instantiation + dependency injection
Tests	6 test files	Logger tests + updated hook tests

Verification

• ✅ TypeScript: tsc --noEmit — 0 errors
• ✅ Tests: 970 pass, 0 fail across 80 files
• ✅ Logger routes: debug/info → stdout, warn → stderr (distinct), error → stderr