Add hooks extension family across harnesses (+ Antigravity harness support)

[execsumo]

Summary

Adds a hooks extension family to Skill Manager, harmonized across harnesses, following the existing MCP family architecture. Hooks are stored as normalized records using canonical events (pre_tool_use, post_tool_use, user_prompt_submit, session_start, stop, pre_compact) and canonical tool categories (shell, file_read, file_write, mcp, web, any); each harness codec translates a canonical record into that harness's native event names and config shape and merges it in under managed-state + content-hash tracking.

Because the hooks family includes hooks-for-Antigravity, this branch also includes the Antigravity (agy) harness integration it depends on. Unrelated fork changes (a light theme, a default data-path change) are intentionally excluded from this PR.

Coverage

Harness	Hooks	Config
Claude Code	Full	~/.claude/settings.json → hooks
Codex	Full	inline [hooks] in ~/.codex/config.toml
Cursor	Full	~/.cursor/hooks.json (category → dedicated event)
OpenCode	Partial	experimental.hook (file-write + stop only)
Antigravity (agy)	Partial	name-keyed ~/.gemini/config/hooks.json

Harnesses differ, so not every canonical event maps everywhere. Skill Manager exposes a representability matrix that surfaces gaps and caveats rather than failing silently — e.g. an Antigravity user_prompt_submit hook maps to PreInvocation, which fires before every model invocation (not only on prompt submit), and that caveat is shown in the UI.

Safety / managed-state

Skill Manager owns only the hook entries it writes. Merges preserve foreign hooks and unrelated config keys (verified per harness for each distinct file shape: subtree JSON, inline TOML, version-wrapped JSON, experimental.hook, and name-keyed maps). Managed entries are tracked by content hash; out-of-band edits surface as drifted; pre-existing harness hooks surface as unmanaged for review. Empty/whitespace/malformed config is handled without raising.

Testing

All green locally:

• Backend: 400 tests pass (bash scripts/test_backend.sh)
• Frontend: 247/247 pass (npm test)
• npm run typecheck: clean
• npm run build: clean

Coverage includes per-harness canonical↔native round-trips, foreign-entry preservation against each file shape, representability gaps/caveats, drift detection, and malformed-config handling, plus a manual cross-harness verification under an isolated HOME.

🤖 Generated with Claude Code

[chzh12]

Thanks for the PR. I’m not comfortable approving this in the current form.

This adds a full new hooks extension family across backend config writers, OpenAPI/generated types, frontend screens, and multiple harness codecs. That is a large new product and architecture surface, so it needs tighter review and a clear design agreement before merge.

I also see concrete correctness risk in the hook identity model. Some harness mappers appear to key native hook updates/removals by command when the native format does not store an id. That means two different managed hooks using the same command but different events or matchers can overwrite or remove each other. A normalized managed-record model should either preserve identity across those cases or explicitly reject duplicate command shapes with tests.

This PR also inherits the Antigravity managed-location test inconsistency from the Antigravity branch: the label ordering adds Antigravity before Codex while the next assertion still expects that index to point at the Codex root.

Please address the identity/overwrite behavior, fix the inherited Antigravity assertion issue, and consider breaking this into smaller reviewable PRs before it moves forward.