feat(chat-ao): add CMA bridge controller subclass

[anfibiacreativa]

│ Stacked on PR 1 (feat/chat-ao-controller-decouple). Base this PR on that branch; rebase onto main once PR 1 merges.

Summary

• Add CmaChatController extends BaseChatController — the CMA bridge path now has its own controller instead of sharing the AO-direct one.
• Route the bridge socket with activationKey + x-site on one AUTH frame, map bridge auth rejections to tester-facing copy, route the skills catalog to the bridge, and
  resume the last session per-site on reload.
• chat-ao.js selects the subclass from the ew.altHarness flag once config resolves.
• 10 new CMA tests; 326 chat-ao tests pass total.

Why

Completes the controller decoupling started in PR 1. With a dedicated CMA subclass, bridge-path behavior (resume, auth-error copy, skills routing) can evolve without
any risk to the CX Coworker path, and vice-versa. It also absorbs the long-lived ewoncma branch's CMA client work onto current main and folds in the reload-resume
change (superseding feat/chat-ao-resume-main).

What Changed

• cma-chat-controller.js (new) — CmaChatController extends Base:
  • _connectionInfo: routes to CMA_BRIDGE_WS_BASE; the AUTH frame carries both x-site (S12 per-site session scoping) and activationKey (bridge auth/routing).
  • friendlyBackendError: maps the bridge's terse auth rejections to tester-facing copy (S15), surfaced only during an active turn.
  • _fetchSkills: routes the catalog to the bridge via the activation key.
  • Reload-resume: a per-site sessionStorage pointer (nx2:cma-episode:/); loadEpisodes reconnects to it (the bridge replays history on attach),
    _onSessionReady persists it, _onSessionError drops a rejected/stale pointer and starts fresh, startNewEpisode clears it.
• base-chat-controller.js — _attach/reattachIfIdle and a default attach-only warmSession move to Base (both harnesses use them via chat-ao.js); Coworker keeps its REST
  warm override.
• chat-ao.js — controller creation deferred until ew.altHarness is known, then new (altHarness ? CmaChatController : CoworkerChatController)(...); the activation key is
  passed through. onUpdate handling extracted to _onControllerUpdate.
• utils/skills.js — fetchSkills routes to the bridge REST plane (+ explicit x-user-id) when an activation key is present; the AO path is byte-unchanged.
• ao-constants.js — CMA bridge WS/HTTP bases.

Test Plan

• test/nx2/blocks/chat-ao/** — 326 tests pass (316 existing + 10 new CMA-subclass tests).
• ESLint clean; secrets scan clean over the branch diff.
• On an ew.altHarness site: send a message, reload the page — the conversation resumes (bridge replays). Start a new session, reload — no stale resume.
• Bad/missing activation key surfaces the friendly copy, not an internal error.
• Skills slash-menu populates from the bridge on the alt harness.
• Regression: a non-alt-harness (CX Coworker) site behaves exactly as before.

Risks / Follow-ups

• Risk: low-moderate — the AO/Coworker path is unchanged and fully covered; the new behavior is isolated to the CMA subclass and its own tests. The one cross-cutting
  change is deferring controller creation to after the flag resolves (no component-mount test depends on the old eager timing).
• Follow-up: the alt-harness +menu customizations were ewoncma-specific against a different menu structure and don't map cleanly to current main; port separately if
  still wanted.
• Follow-up: land the stop-indicator (feat/chat-ao-stop-indicator) into BaseChatController.
• Retires ewoncma as a long-lived branch once merged.

Test URLs:

• Before: https://main--da-nx--adobe.aem.live/
• After: https://feat-chat-ao-cma-subclass--da-nx--adobe.aem.live/

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