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 installed via `uv tool install hermes-agent` lives outside any
venv. `_cmd_update_pip` previously ran `uv pip install --upgrade`, which
errors with `No virtual environment found; run uv venv ...`. The user
hits this on the very first `hermes update` after a standard
non-`--system` install with `uv` on PATH.
Add `is_uv_tool_install()` in `hermes_cli/config.py`: fast path inspects
`sys.prefix` for the standard `uv/tools/hermes-agent/` layout, falls
back to `uv tool list` for non-standard prefixes. Both the
user-facing `recommended_update_command_for_method("pip")` string and
the actual subprocess invocation in `_cmd_update_pip` now switch to
`uv tool upgrade hermes-agent` when detected. Non-tool installs and the
no-`uv` fallback keep their existing commands unchanged.
