feat(#2091): migrate hermes onto EoS imperative adapter + extensionEvents dialect (ADR-1239)

- Fold 7 hardcoded isHermes/runtime === 'hermes' branches in bin/install.js into
  descriptor-driven _hostBehaviors lookups (skillFrontmatterVersion,
  skillsManifestPrefix, trackCategoryDescription, writeCategoryDescription,
  reportSkillsCount, legacyCommandsGsdCleanup, brandingRewrites)
- Add runtime.hostBehaviors block to capabilities/hermes/capability.json
- Register EXTENSION_EVENT_SURFACES.hermes (13 real plugin hook events) in
  src/host-integration.cts — replaces the borrowed hookEvents:'claude' 6-event
  surface that silently never fired on Hermes
- Add extensionEvents:'hermes' to the descriptor
- Add 'hermes' to VALID_EXTENSION_EVENTS in capability-validator.cjs
- Regenerate capability-registry.cjs
- Tests: hermes-imperative-reference (negotiation, axes, fail-closed, source-guard),
  hermes-dispatch-upgrade (dispatch posture, degradation, fail-closed)
- Changeset + docs update

capabilities/hermes/capability.json

@@ -50,6 +50,21 @@
     "writesSharedSettings": true,
     "permissionWriter": null,
     "extendedHookEvents": [],
+    "extensionEvents": "hermes",
+    "hostBehaviors": {
+      "skillFrontmatterVersion": true,
+      "skillsManifestPrefix": "skills/gsd/",
+      "trackCategoryDescription": true,
+      "writeCategoryDescription": true,
+      "reportSkillsCount": true,
+      "legacyCommandsGsdCleanup": true,
+      "brandingRewrites": {
+        "CLAUDE.md": "HERMES.md",
+        "Claude Code": "Hermes Agent",
+        ".claude/": ".hermes/"
+      },
+      "reapplyCommand": "gsd-update --reapply (mention the skill name)"
+    },
     "hostIntegration": {
       "embeddingMode": "imperative",
       "commandSurface": "slash-programmatic",