fix(cli): restrict uv-tool-install detection to running interpreter

Copilot review on PR #29703 flagged two issues with the `uv tool list`
fallback in `is_uv_tool_install`:

1. False positive: `uv tool list` returns the *machine*'s installed
   tools, not the active install. A regular pip/venv Hermes on a host
   that also has `uv tool install hermes-agent` available would be
   misclassified as a uv-tool install, and `hermes update` would
   upgrade the wrong copy.

2. Overhead: the subprocess call (up to a 15s timeout) was triggered
   even from `recommended_update_command_for_method`, which just
   computes a display string.

Restrict detection to properties of the running interpreter
(`sys.prefix` and `sys.executable` — both can carry the uv-tool layout
marker depending on entry point). Drop the `uv tool list` fallback and
the `uv_path` parameter entirely. `_cmd_update_pip` now also surfaces a
clear hint when the runtime looks like a uv-tool install but `uv` is
missing from PATH, instead of silently falling back to `python -m pip`.

hermes_cli/main.py

@@ -8977,11 +8977,13 @@ def _cmd_update_pip(args):
     print("→ Checking PyPI for updates...")
 
     uv = shutil.which("uv")
-    if uv:
-        if is_uv_tool_install(uv):
-            cmd = [uv, "tool", "upgrade", "hermes-agent"]
-        else:
-            cmd = [uv, "pip", "install", "--upgrade", "hermes-agent"]
+    if is_uv_tool_install():
+        if not uv:
+            print("✗ Detected a uv-tool install but `uv` is not on PATH; install uv and retry.")
+            sys.exit(1)
+        cmd = [uv, "tool", "upgrade", "hermes-agent"]
+    elif uv:
+        cmd = [uv, "pip", "install", "--upgrade", "hermes-agent"]
     else:
         cmd = [sys.executable, "-m", "pip", "install", "--upgrade", "hermes-agent"]