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>

src/jarvis/tools/registry.py

@@ -20,6 +20,7 @@ from .builtin.refresh_mcp_tools import RefreshMCPToolsTool
 from .builtin.weather import WeatherTool
 from .builtin.stop import StopTool
 from .builtin.tool_search import ToolSearchTool
+from .builtin.browse_and_play import BrowseAndPlayTool
 from .types import ToolExecutionResult
 from ..config import Settings
 from .external.mcp_client import MCPClient
@@ -39,6 +40,7 @@ BUILTIN_TOOLS = {
     "getWeather": WeatherTool(),
     "stop": StopTool(),
     "toolSearchTool": ToolSearchTool(),
+    "browseAndPlay": BrowseAndPlayTool(),
 }
 
 # Global MCP tools cache