feat: complete Gemma 4 browser_vision wiring — task routing, timeout, tests

Building on the Gemma 4 default already on this branch:

- Change call_llm() task from "vision" to "browser_vision" in browser_vision()
  so auxiliary.browser_vision.* config is consulted for provider/model/timeout
- Route call_llm(task="browser_vision") through the vision provider resolution
  path in auxiliary_client.py (same as task="vision")
- Fix timeout resolution: check auxiliary.browser_vision.timeout before
  auxiliary.vision.timeout (allows browser-specific timeout override)
- Add timeout option to auxiliary.browser_vision in cli-config.yaml.example
- Add test_browser_vision_gemma4.py covering: task routing assertions,
  call_llm() vision branch routing, and timeout config key ordering

Refs #816

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cli-config.yaml.example

@@ -363,6 +363,7 @@ compression:
 #   # Can also be overridden per-session with BROWSER_VISION_MODEL env var.
 #   browser_vision:
 #     model: "google/gemma-4-27b-it"  # default; override e.g. "google/gemini-2.5-flash"
+#     timeout: 120                     # API call timeout in seconds (default 120s)
 #
 #   # Web page scraping / summarization + browser page text extraction
 #   web_extract: