refactor: remove browser_close tool — auto-cleanup handles it

The browser_close tool was called in only 9% of browser sessions (13/144
navigations across 66 sessions), always redundantly — cleanup_browser()
already runs via _cleanup_task_resources() at conversation end, and the
background inactivity reaper catches anything else.

Removing it saves one tool schema slot in every browser-enabled API call.

Also fixes a latent bug: cleanup_browser() now handles Camofox sessions
too (previously only Browserbase). Camofox sessions were never auto-cleaned
per-task because they live in a separate dict from _active_sessions.

Files changed (13):
- tools/browser_tool.py: remove function, schema, registry entry; add
  camofox cleanup to cleanup_browser()
- toolsets.py, model_tools.py, prompt_builder.py, display.py,
  acp_adapter/tools.py: remove browser_close from all tool lists
- tests/: remove browser_close test, update toolset assertion
- docs/skills: remove all browser_close references

website/docs/user-guide/features/browser.md

@@ -277,10 +277,6 @@ Check the browser console for any JavaScript errors
 
 Use `clear=True` to clear the console after reading, so subsequent calls only show new messages.
 
-### `browser_close`
-
-Close the browser session and release resources. Call this when done to free up Browserbase session quota.
-
 ## Practical Examples
 
 ### Filling Out a Web Form
@@ -295,7 +291,6 @@ Agent workflow:
 4. browser_type(ref="@e5", text="SecurePass123")
 5. browser_click(ref="@e8")  → clicks "Create Account"
 6. browser_snapshot()  → confirms success
-7. browser_close()
 ```
 
 ### Researching Dynamic Content
@@ -307,7 +302,6 @@ Agent workflow:
 1. browser_navigate("https://github.com/trending")
 2. browser_snapshot(full=true)  → reads trending repo list
 3. Returns formatted results
-4. browser_close()
 ```
 
 ## Session Recording
@@ -349,5 +343,5 @@ If paid features aren't available on your plan, Hermes automatically falls back
 - **Text-based interaction** — relies on accessibility tree, not pixel coordinates
 - **Snapshot size** — large pages may be truncated or LLM-summarized at 8000 characters
 - **Session timeout** — cloud sessions expire based on your provider's plan settings
-- **Cost** — cloud sessions consume provider credits; use `browser_close` when done. Use `/browser connect` for free local browsing.
+- **Cost** — cloud sessions consume provider credits; sessions are automatically cleaned up when the conversation ends or after inactivity. Use `/browser connect` for free local browsing.
 - **No file downloads** — cannot download files from the browser