fix(plugins): show entry-point plugins in 'hermes plugins list' (#58644)

[iacker]

What does this PR do?

hermes plugins list did not show pip-installed plugins registered via the
hermes_agent.plugins entry-point group. Those plugins are loaded and
active (the real loader PluginManager.discover_and_load() scans entry
points) — they were just invisible in the listing, including --json and
--plain output.

Root cause: two separate discovery paths. The loader scans directories and
entry points; the display helper _discover_all_plugins() in
hermes_cli/plugins_cmd.py scanned only bundled + user directories.

Related Issue

Fixes #58644

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• hermes_cli/plugins_cmd.py — _discover_all_plugins() now also scans
  entry-point plugins by reusing PluginManager._scan_entry_points()
  (rather than duplicating the importlib.metadata logic). Entry-point
  plugins have no directory, so their tuple carries dir_path=None; the
  render, filter, and resolve paths already ignore that element. setdefault
  keeps directory plugins winning on key collision, matching
  discover_and_load() precedence.
• tests/hermes_cli/test_plugins_cmd_list.py — regression test asserting an
  entry-point plugin surfaces in the display path and resolves for
  enable/disable, with dir_path=None.

How to Test

Reproduce (before fix): a pip plugin registering a hermes_agent.plugins
entry point (e.g. rtk-hermes) is loaded and rewriting commands, but absent
from hermes plugins list / --json / --plain.

Automated:

pytest tests/hermes_cli/test_plugins_cmd_list.py -q

The new test_discover_all_plugins_includes_entry_points fails on main
(entry points never reach the display path) and passes with this change.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix
• I've run the impacted tests and all pass (125 passed across the three
  plugins_cmd suites)
• I've added tests for my changes
• I've tested on my platform: macOS 26.5.1, Python 3.13

Documentation & Housekeeping

• N/A — no docs/config/schema/tool-behavior changes

[alt-glitch]

This was generated by AI during triage.

Duplicate of #23814 (earliest-open canonical) — same fix: mirror PluginManager._scan_entry_points() into _discover_all_plugins() so pip-installed entry-point plugins show in hermes plugins list. This is also the exact same change as the same-day twin #58645. Consolidating on #23814; keeping #58644 open as the issue.

[iacker]

Closing as duplicate of #23814 per triage bot — canonical PR addresses the same issue.