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.

tests/hermes_cli/test_setup_openclaw_migration.py

@@ -419,7 +419,12 @@ class TestGetSectionConfigSummary:
                 return "disc456"
             return ""
 
-        with patch.object(setup_mod, "get_env_value", side_effect=env_side):
+        # Also patch gateway module's binding since _platform_status()
+        # reads from hermes_cli.gateway.get_env_value after the setup
+        # flows were unified via platform_registry.
+        import hermes_cli.gateway as gateway_mod
+        with patch.object(setup_mod, "get_env_value", side_effect=env_side), \
+             patch.object(gateway_mod, "get_env_value", side_effect=env_side):
             result = setup_mod._get_section_config_summary({}, "gateway")
         assert "Telegram" in result
         assert "Discord" in result
@@ -471,7 +476,9 @@ class TestGetSectionConfigSummary:
         def env_side(key):
             return "true" if key == "WHATSAPP_ENABLED" else ""
 
-        with patch.object(setup_mod, "get_env_value", side_effect=env_side):
+        import hermes_cli.gateway as gateway_mod
+        with patch.object(setup_mod, "get_env_value", side_effect=env_side), \
+             patch.object(gateway_mod, "get_env_value", side_effect=env_side):
             result = setup_mod._get_section_config_summary({}, "gateway")
         assert result is not None
         assert "WhatsApp" in result
@@ -481,7 +488,9 @@ class TestGetSectionConfigSummary:
         def env_side(key):
             return "http://signal.local" if key == "SIGNAL_HTTP_URL" else ""
 
-        with patch.object(setup_mod, "get_env_value", side_effect=env_side):
+        import hermes_cli.gateway as gateway_mod
+        with patch.object(setup_mod, "get_env_value", side_effect=env_side), \
+             patch.object(gateway_mod, "get_env_value", side_effect=env_side):
             result = setup_mod._get_section_config_summary({}, "gateway")
         assert result is not None
         assert "Signal" in result
@@ -539,9 +548,18 @@ class TestGetSectionConfigSummary:
             env_var = plat.get("token_var")
             if not env_var:
                 continue
+            # Some platforms require a specific value shape (e.g. WhatsApp
+            # needs the literal "true"). Use a sentinel that satisfies every
+            # real validator _platform_status() currently checks.
             def env_side(key, _target=env_var):
-                return "x" if key == _target else ""
-            with patch.object(setup_mod, "get_env_value", side_effect=env_side):
+                if key != _target:
+                    return ""
+                if _target == "WHATSAPP_ENABLED":
+                    return "true"
+                return "x"
+            import hermes_cli.gateway as gateway_mod
+            with patch.object(setup_mod, "get_env_value", side_effect=env_side), \
+                 patch.object(gateway_mod, "get_env_value", side_effect=env_side):
                 result = setup_mod._get_section_config_summary({}, "gateway")
             expected = setup_mod._gateway_platform_short_label(label)
             assert result is not None, f"{label} ({env_var}) not recognised"