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

.changeset/2091-eos-hermes-imperative-adapter.md

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+---
+type: Changed
+pr: 0
+---
+**Hermes Agent is now driven through the public Host-Integration Interface, with three capability upgrades (ADR-1239 / EoS).** Hermes previously installed via hardcoded `runtime === 'hermes'`/`isHermes` branches in `bin/install.js`; its install/uninstall now runs through the imperative adapter, and every hardcoded hermes branch is folded into descriptor-driven `runtime.hostBehaviors`. Three upgrades land: (1) **real plugin hook vocabulary** — GSD registers a new `extensionEvents: "hermes"` dialect carrying the 13 documented Hermes plugin events (`pre_tool_call`, `post_tool_call`, `pre_llm_call`, `post_llm_call`, `on_session_start`, `on_session_end`, `on_session_finalize`, `on_session_reset`, `subagent_start`, `subagent_stop`, `pre_gateway_dispatch`, `pre_approval_request`, `transform_tool_result`), replacing the borrowed `hookEvents: "claude"` 6-event surface that silently never fired; cite https://github.com/nousresearch/hermes-agent/blob/main/website/docs/user-guide/features/hooks.md. (2) **dispatch posture** — Hermes' `dispatch.nested: true` with `maxDepth: 1` is correctly negotiated (not silently flattened). (3) **branding/category metadata** — `DESCRIPTION.md` category descriptions, `version:` frontmatter, and branding rewrites are now descriptor-driven rather than hardcoded. Install/uninstall output is byte-identical (golden parity asserted for all runtimes). (#2091)