refactor(plugins): drop dead bundled-source guard in _discover_all_plugins

The `if key in seen and source == "bundled": continue` check was
unreachable: bundled is scanned before user, so `key in seen` can never
be true while `source == "bundled"`. The "user overrides bundled"
semantics are preserved automatically by the unconditional
`seen[key] = …` on the user pass.

Replaces the dead guard with a one-line comment explaining the
overwrite semantics, so a future contributor adding a third source
(e.g. project plugins) can see at a glance how ordering interacts with
the dict-overwrite. Matches `PluginManager.discover_and_load`'s
"user wins" rule.

Spotted by Copilot in code review on #27161.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hermes_cli/plugins_cmd.py

@@ -762,11 +762,12 @@ def _discover_all_plugins() -> list:
                     except Exception:
                         pass
                 key = f"{prefix}/{d.name}" if prefix else manifest_name
-                if key in seen and source == "bundled":
-                    continue
                 src_label = source
                 if source == "user" and (d / ".git").exists():
                     src_label = "git"
+                # Bundled is scanned before user, so the user pass overwrites
+                # bundled entries with the same key — matches
+                # PluginManager.discover_and_load's "user wins" semantics.
                 seen[key] = (key, version, description, src_label, d)
                 continue