fix(update): handle pipx installs + --system fallback in _cmd_update_pip

Extends the uv-tool detection (briandevans, #29703) to cover the
remaining no-venv install layouts that hit the same uv 'No virtual
environment found' error:

- pipx-managed installs (sys.prefix under .../pipx/...) -> 'pipx upgrade',
  matching scripts/auto-update.sh (pipx-detection idea from
  inchargeautomation-lab, #29852)
- bare pip outside any venv -> 'uv pip install --system --upgrade'
- venv (launcher shim) keeps the VIRTUAL_ENV overlay from #35224 and never
  gets --system, so the install always targets the venv, not system Python

The four branches are mutually exclusive; VIRTUAL_ENV is exported only for
the uv-pip-in-venv path (uv tool / pipx upgrade ignore it).

Co-authored-by: Joshua Kimbrell <incharge.automation@gmail.com>

hermes_cli/main.py

@@ -8977,19 +8977,43 @@ def _cmd_update_pip(args):
     print("→ Checking PyPI for updates...")
 
     uv = shutil.which("uv")
+    in_venv = sys.prefix != sys.base_prefix
+    # pipx-managed installs live under .../pipx/venvs/<name>/...
+    pipx_managed = "pipx" in sys.prefix.split(os.sep)
+    pipx = shutil.which("pipx") if pipx_managed else None
+
+    # Only the ``uv pip install`` path inside a venv needs VIRTUAL_ENV
+    # exported (uv refuses to install without it when the launcher shim
+    # didn't activate the venv). ``uv tool upgrade`` / ``pipx upgrade``
+    # operate on a named environment and ignore VIRTUAL_ENV, so we don't
+    # set it for them.
+    export_virtualenv = False
+
     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 pipx_managed and pipx:
+        # pipx owns its own venv; ``pipx upgrade`` is the only correct path.
+        # Matches scripts/auto-update.sh, which already uses pipx upgrade.
+        cmd = [pipx, "upgrade", "hermes-agent"]
     elif uv:
         cmd = [uv, "pip", "install", "--upgrade", "hermes-agent"]
+        if in_venv:
+            # Launcher shim runs the venv interpreter but doesn't export
+            # VIRTUAL_ENV; without it uv errors "No virtual environment found".
+            export_virtualenv = True
+        else:
+            # Outside any venv, ``--system`` lets uv target the active
+            # interpreter, matching pip's default behaviour.
+            cmd.insert(3, "--system")
     else:
         cmd = [sys.executable, "-m", "pip", "install", "--upgrade", "hermes-agent"]
 
     print(f"→ Running: {' '.join(cmd)}")
     run_kwargs = {}
-    if sys.prefix != sys.base_prefix:
+    if export_virtualenv:
         run_kwargs["env"] = {**os.environ, "VIRTUAL_ENV": sys.prefix}
     result = subprocess.run(cmd, **run_kwargs)
     if result.returncode != 0: