fix(windows): auto-install Playwright Chromium + surface it in doctor

scripts/install.sh runs 'npx playwright install --with-deps chromium'
on every Linux distro after the npm-install step, which is why browser
tools Just Work on Linux.  scripts/install.ps1 never did the equivalent
step, so on native Windows installs check_browser_requirements() in
tools/browser_tool.py would return False (no Chromium under
%LOCALAPPDATA%\ms-playwright) and every browser_* tool got silently
filtered out of the agent's tool schema — no error, no log entry, user
just wondered why the tools didn't exist.

Two-part fix:

1. scripts/install.ps1: after 'npm install' in InstallDir succeeds, run
   'npx playwright install chromium'.  Resolves npx via the same
   execution-policy-aware logic already used for npm (prefer npx.cmd
   next to npmExe, fall back to Get-Command).  Surfaces a warning +
   manual-recovery hint when the install fails, matching install.sh
   behaviour for distros.

2. hermes_cli/doctor.py: after the agent-browser check, lazily import
   tools.browser_tool and reuse the exact same _chromium_installed()
   predicate check_browser_requirements() uses, so the doctor signal
   cannot drift from the runtime gate.  Skip the check when Camofox /
   CDP override / a cloud provider / Lightpanda is configured (those
   bypass local Chromium).  On missing Chromium, the hint is
   platform-correct: '--with-deps' on POSIX, plain 'install chromium'
   on win32.

Verified on Windows 10:
- 'npx playwright install chromium' completes successfully, drops
  Chrome Headless Shell under %LOCALAPPDATA%\ms-playwright
- check_browser_requirements() flips from False -> True
- 'hermes doctor' now prints either '✓ Playwright Chromium (browser
  engine)' or '⚠ Playwright Chromium not installed' + fix command
- tests/hermes_cli/test_doctor.py: 38/38 pass
- tests/tools/test_browser_chromium_check.py: 16/16 pass

hermes_cli/doctor.py

@@ -1035,10 +1035,13 @@ def run_doctor(args):
         check_ok("Node.js")
         # Check if agent-browser is installed
         agent_browser_path = PROJECT_ROOT / "node_modules" / "agent-browser"
+        agent_browser_ok = False
         if agent_browser_path.exists():
             check_ok("agent-browser (Node.js)", "(browser automation)")
+            agent_browser_ok = True
         elif shutil.which("agent-browser"):
             check_ok("agent-browser", "(browser automation)")
+            agent_browser_ok = True
         else:
             if _is_termux():
                 check_info("agent-browser is not installed (expected in the tested Termux path)")
@@ -1048,6 +1051,56 @@ def run_doctor(args):
                     check_info(step)
             else:
                 check_warn("agent-browser not installed", "(run: npm install)")
+
+        # Chromium presence — the browser tools silently fail to register when
+        # agent-browser is found but no Playwright-managed Chromium is on disk
+        # (tools/browser_tool.py::check_browser_requirements filters them out
+        # before the agent ever sees them).  Reuse the exact predicate it uses
+        # so the two checks cannot diverge.  Skip on Termux (not a tested
+        # path).
+        if agent_browser_ok and not _is_termux():
+            try:
+                # Lazy import: browser_tool is a ~150KB module we don't want
+                # to eagerly load in every `hermes doctor` invocation.
+                from tools.browser_tool import (
+                    _chromium_installed,
+                    _is_camofox_mode,
+                    _get_cloud_provider,
+                    _get_cdp_override,
+                    _using_lightpanda_engine,
+                )
+            except Exception:
+                # If browser_tool can't even import, that's a separate bug
+                # surfaced elsewhere; don't crash doctor.
+                pass
+            else:
+                # Only warn about Chromium if the installed engine actually
+                # requires it: Camofox, CDP override, a cloud provider, or
+                # Lightpanda all bypass the local Chromium requirement.
+                skip_chromium_check = (
+                    _is_camofox_mode()
+                    or bool(_get_cdp_override())
+                    or _get_cloud_provider() is not None
+                    or _using_lightpanda_engine()
+                )
+                if not skip_chromium_check:
+                    if _chromium_installed():
+                        check_ok("Playwright Chromium", "(browser engine)")
+                    else:
+                        check_warn(
+                            "Playwright Chromium not installed",
+                            "(browser_* tools will be hidden from the agent)",
+                        )
+                        if sys.platform == "win32":
+                            check_info(
+                                f"Install with: cd {PROJECT_ROOT} && "
+                                "npx playwright install chromium"
+                            )
+                        else:
+                            check_info(
+                                f"Install with: cd {PROJECT_ROOT} && "
+                                "npx playwright install --with-deps chromium"
+                            )
     else:
         if _is_termux():
             check_info("Node.js not found (browser tools are optional in the tested Termux path)")