feat(acp): hermes acp --setup-browser bootstraps browser tools for registry installs

The Zed ACP Registry path (uvx --from 'hermes-agent[acp]==X' hermes-acp)
gets a Python-only install. Browser tools depend on the agent-browser npm
package + Chromium, neither of which are in the wheel. Without an
explicit bootstrap, registry users have no path to working browser tools.

Ship a bundled, idempotent bootstrap script (Linux/macOS bash + Windows
PowerShell) inside acp_adapter/bootstrap/ as wheel package-data. New
entry points:

  hermes acp --setup-browser        # interactive; prompts before Chromium download
  hermes acp --setup-browser --yes  # non-interactive
  hermes-acp --setup-browser

The terminal-auth flow (hermes acp --setup) also offers the browser
bootstrap as a follow-up after model selection, so first-run registry
users get the option without knowing the flag exists.

Key design choices:
- npm install -g --prefix $NODE_PREFIX so we never need sudo. System Node
  on PATH is respected; only the install target is redirected to the
  user-writable Hermes-managed Node prefix.
- tools/browser_tool.py::_browser_candidate_path_dirs() already walks
  $HERMES_HOME/node/bin, so installed binaries are discovered with no
  agent-side code change.
- System Chrome/Chromium detection short-circuits the ~400 MB Playwright
  download when a suitable browser already exists.
- Bash + PowerShell live as ONE copy each under acp_adapter/bootstrap/.
  Not duplicated under scripts/. install.sh and install.ps1 keep their
  inline browser blocks for the source-checkout path.

E2E validated end-to-end:
  bash bootstrap_browser_tools.sh --skip-chromium
    → installs agent-browser into ~/.hermes/node/bin/
  tools.browser_tool._find_agent_browser()
    → returns the installed path
  check_browser_requirements()
    → returns True (browser tools register)

Tests:
- tests/acp/test_entry.py: 11 tests covering --setup-browser dispatch
  (linux + windows + --yes forwarding + failure propagation), the
  terminal-auth follow-up prompt path, and a package-data wheel-shipping
  assertion that catches any future pyproject.toml regression.

Docs: website/docs/user-guide/features/acp.md gains a 'Browser tools
(optional)' subsection with the two-line install + what-it-does.

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

@@ -78,6 +78,27 @@ hermes acp --version
 hermes acp --check
 ```
 
+### Browser tools (optional)
+
+Browser tools (`browser_navigate`, `browser_click`, etc.) depend on the
+`agent-browser` npm package and Chromium, which aren't part of the Python
+wheel. Install them with:
+
+```bash
+hermes acp --setup-browser           # interactive (prompts before ~400 MB download)
+hermes acp --setup-browser --yes     # accept the download non-interactively
+```
+
+This is the standalone command. The Zed registry's terminal-auth flow (`hermes acp --setup`) also offers the browser bootstrap as a follow-up question after model selection, so most users never need to run `--setup-browser` directly.
+
+What it does:
+
+- Installs Node.js 22 LTS into `~/.hermes/node/` if missing
+- `npm install -g agent-browser @askjo/camofox-browser` into that prefix (no sudo needed — `npm`'s `--prefix` points at the user-writable Hermes-managed Node)
+- Installs Playwright Chromium, or uses a detected system Chrome/Chromium when available
+
+The bootstrap is idempotent — re-running it is fast and skips work that's already done.
+
 ## Editor setup
 
 ### VS Code