feat(plugins): bundled platform plugins auto-load by default

Platform plugins shipped in-repo under plugins/platforms/ should be
available out of the box — users shouldn't have to add 'irc-platform'
to plugins.enabled before they can pick IRC from the gateway setup menu.

Adds a new ``kind: platform`` plugin type that mirrors the existing
``kind: backend`` auto-load semantics:

- Bundled (shipped in the hermes-agent repo): auto-load unconditionally.
- User-installed (~/.hermes/plugins/): still opt-in via plugins.enabled
  so untrusted code doesn't silently run.

Changes:

* hermes_cli/plugins.py: add 'platform' to _VALID_PLUGIN_KINDS, document
  the new kind in the PluginManifest docstring, extend the bundled auto-
  load rule from 'backend only' to 'backend or platform'.

* plugins/platforms/irc/plugin.yaml: declare kind: platform.

* hermes_cli/gateway.py: remove the now-redundant
  _load_bundled_platform_plugins_for_enumeration() helper and the
  _enable_plugin_for_platform() helper. The setup menu's _all_platforms()
  just calls discover_plugins() and reads the registry — bundled
  platforms are already loaded at that point. Drops the 'needs_enable'
  flag and the 'plugin disabled — select to enable' status string.

* hermes_cli/setup.py: relax the "gateway is configured" detector used
  during OpenClaw migration. Switching to _platform_status() in an
  earlier commit tightened the check to require an exact "configured"
  match, dropping platforms whose status is "enabled, not paired",
  "partially configured", "configured + E2EE", etc. Now any non-"not
  configured" status counts — the user has already started setup there
  and we shouldn't force the section to rerun.

* tests/hermes_cli/test_setup_irc.py: drop the TestIRCPluginDisabledFlow
  class and test_configure_platform_enables_disabled_plugin_first — the
  no-longer-existent flow they were testing.

* tests/hermes_cli/test_setup_openclaw_migration.py: patch both
  setup.get_env_value and gateway.get_env_value in the 4 gateway-section
  tests that reach _platform_status() through the unified setup flow;
  switch WHATSAPP_ENABLED to the literal "true" in the registry-parity
  test so WhatsApp's value-shape validator matches.

Verified via fresh-install smoke (empty plugins.enabled, no env vars):
IRC plugin loads, Platform('irc') resolves, _all_platforms() lists IRC
with status 'not configured'. 160 targeted tests pass.

hermes_cli/plugins.py

@@ -170,7 +170,7 @@ def _get_enabled_plugins() -> Optional[set]:
 # Data classes
 # ---------------------------------------------------------------------------
 
-_VALID_PLUGIN_KINDS: Set[str] = {"standalone", "backend", "exclusive"}
+_VALID_PLUGIN_KINDS: Set[str] = {"standalone", "backend", "exclusive", "platform"}
 
 
 @dataclass
@@ -196,6 +196,11 @@ class PluginManifest:
     #              Selection via ``<category>.provider`` config key; the
     #              category's own discovery system handles loading and the
     #              general scanner skips these.
+    # ``platform``: gateway messaging platform adapter (e.g. IRC). Bundled
+    #              platform plugins auto-load so every shipped platform is
+    #              available out of the box; user-installed platform plugins
+    #              in ~/.hermes/plugins/ still gated by ``plugins.enabled``
+    #              (untrusted code).
     kind: str = "standalone"
     # Registry key — path-derived, used by ``plugins.enabled``/``disabled``
     # lookups and by ``hermes plugins list``. For a flat plugin at
@@ -705,7 +710,11 @@ class PluginManager:
             # just work. Selection among them (e.g. which image_gen backend
             # services calls) is driven by ``<category>.provider`` config,
             # enforced by the tool wrapper.
-            if manifest.kind == "backend" and manifest.source == "bundled":
+            #
+            # Bundled platform plugins (gateway adapters like IRC) auto-load
+            # for the same reason: every platform Hermes ships must be
+            # available out of the box without the user having to opt in.
+            if manifest.source == "bundled" and manifest.kind in ("backend", "platform"):
                 self._load_plugin(manifest)
                 continue