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

docs/reference/host-integration-capability-matrix.md

@@ -258,6 +258,8 @@ Sources consulted:
 - https://github.com/NousResearch/hermes-agent/releases/tag/v2026.6.19
 - /nousresearch/hermes-agent (Context7)
 
+**EoS migration status (#2091):** Migrated onto the imperative adapter. All `runtime === 'hermes'` branches in `bin/install.js` folded into descriptor-driven `runtime.hostBehaviors`. New `extensionEvents: "hermes"` dialect registered (13 real plugin hook events, replacing the borrowed `hookEvents: "claude"` 6-event surface). Cite: https://github.com/nousresearch/hermes-agent/blob/main/website/docs/user-guide/features/hooks.md
+
 Documentation gaps:
 - runtime — Hermes plugins and agent core run in Python, but this was confirmed by code inspection rather than explicit docs statement.
 - dispatch.namedDispatch — docs explicitly confirm no named-agent dispatch in delegate_task; Kanban has named profiles but that is a separate board system not a dispatch mechanism.