feat(brain): wire STREAM_BROWSER real-time modes into the reply engine (browser + Gemini)

Completes the two info modes in the Python brain:

- config.py: read STREAM_BROWSER / GEMINI_API_KEY / GEMINI_MODEL from env into
  Settings (stream_browser, gemini_api_key, gemini_model). Verified load_settings
  reads both modes.
- realtime_search.py: two fail-open backends returning the same fenced
  UNTRUSTED-WEB-EXTRACT envelope: browser_search() shells the Node CDP helper to
  drive the on-screen Chrome (visible on the broadcast); gemini_search() calls
  the Gemini REST API with google_search grounding.
- web_search.run(): routes by mode before the DDG cascade (true->browser,
  false->Gemini), falling through to DDG/Brave/Wikipedia on any miss.
- browse_and_play tool: plays a YouTube video on the shared screen (true mode
  only); registered in the tool registry.
- specs + docs/llm_contexts.md updated (new Gemini LLM context); CLAUDE.md spec
  registry updated.

Verified live against the running Chrome: true-mode webSearch returned real
Google results for "오늘 서울 날씨", browseAndPlay played the IU 밤편지 MV, and
false-mode degrades gracefully on a bad/absent key. A valid GEMINI_API_KEY is
still needed to confirm the real Gemini grounding output.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CLAUDE.md

@@ -21,7 +21,8 @@ Any code change must either adhere to our spec files perfectly or you should ask
 | `src/jarvis/tools/builtin/tool_search.spec.md` | toolSearchTool escape hatch for mid-loop tool routing | Re-runs the same router; never removes stop/self; capped per reply |
 | `src/jarvis/tools/external/mcp_runtime.spec.md` | Persistent MCP runtime: per-server long-lived stdio session, queue-based dispatch, retry on transient session loss | One worker per server keyed by config; calls to the same server serialise; `MCPServerSessionError` for session-level failures; opt-in `idle_timeout_sec` for stateless servers |
 | `src/jarvis/reply/prompts/prompts.spec.md` | System/user prompt templates | — |
-| `src/jarvis/tools/builtin/web_search.spec.md` | webSearch tool: cascade fetch, SSRF guard, prompt-injection fence, links-only envelope | Untrusted web content is fenced as data, not instructions; rank preference over speed; honest failure over confabulation |
+| `src/jarvis/tools/builtin/web_search.spec.md` | webSearch tool: STREAM_BROWSER routing (browser/Gemini), cascade fetch, SSRF guard, prompt-injection fence, links-only envelope | Untrusted web content is fenced as data, not instructions; rank preference over speed; honest failure over confabulation |
+| `src/jarvis/tools/builtin/browse_and_play.spec.md` | browseAndPlay tool: play YouTube on the shared screen (screen-share mode only) | Node layer owns Chrome/CDP; mode-gated; fail-open, no LLM call |
 | `src/jarvis/tools/builtin/nutrition/log_meal.spec.md` | logMeal tool: single-property schema for planner fast-path, internal nutrition extraction, untrusted-data fence, follow-ups | Public schema is a single optional `meal` string; nutrition fields are internal; user text is fenced as data |
 | `src/jarvis/utils/location.spec.md` | GeoIP location detection | Privacy-first; local GeoLite2 DB only |
 | `src/jarvis/memory/graph.spec.md` | Node graph memory (v2), self-organising tree, UI explorer | Dynamic structure; access-aware; auto-split/merge (future) |