v0.4.0: agy provider swap, port auto-kill, apscheduler auto-install, chat history + file uploads, memory knowledge graph, diff viewer, cache/layout fixes, 74 tests
- Replace Gemini CLI with agy (Antigravity) across backend, routing, frontend, skills, docs
- start.sh: kill stale process on target port; scheduler.py: auto-install apscheduler
- Chat History page (q/agent/limit search), /api/chat/upload with 2MB allowlist + 24h TTL
- /api/memory/graph knowledge graph, /api/diff code diff viewer
- Fix stale-cache 404s, zoom-proof layout, tab-bar collapse, skill count
- 15 new isolated tests (59 -> 74)
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