fix(agents): keep disabled custom agents visible in settings

[szafranski]

What

Keep user-disabled custom agents visible (greyed, with a working re-enable toggle) in
Settings → Agents → Local Agents, instead of having them vanish from the whole UI.

Fixes #3318

Why

Toggling a custom agent off removed it from the entire UI, including the settings list that
hosts the re-enable toggle — so there was no way to turn it back on from the GUI. The
settings screen shared the same /api/agents data path as the pickers, so when the backend
dropped the disabled row it disappeared everywhere.

How

The fix keeps pickers untouched and gives the settings surface its own data path:

• ipcBridge.ts: new sibling getManagedAgents bridge hitting
  /api/agents?include_disabled=true. getAvailableAgents (the picker path) is unchanged.
• agentTypes.ts: new MANAGED_AGENTS_SWR_KEY + fetchManagedAgents, kept separate from
  the shared DETECTED_AGENTS_SWR_KEY so disabled agents never leak into the pickers.
• useAgents.ts: new useManagedAgents() hook. Its revalidate refreshes both the
  management key and the shared detected key, so toggling an agent on/off in settings is
  immediately reflected in every picker.
• LocalAgents.tsx: switched from useAgents() to useManagedAgents() so disabled custom
  agents stay listed. The existing toggle/create/delete handlers already call this hook's
  revalidate, so both caches stay in sync.
• AgentCard.tsx: a disabled custom card now greys its identity block (subtle opacity) in
  addition to the already-disabled Start Chat button.

No new user-facing strings (the greyed state + disabled button communicate the state), so no
i18n changes.

Tests

bunx vitest run — added:

• useManagedAgents: subscribes to the management key, and revalidate /
  refreshCustomAgents refresh both SWR keys (this is what makes a re-enabled agent
  reappear in pickers).
• fetchManagedAgents: hits the include_disabled bridge (never the picker-safe one) and
  degrades to [] on failure / non-array.

Local checks

• bun run format — clean
• bun run lint — 0 errors (pre-existing warnings only)
• bunx tsc --noEmit — clean
• node scripts/check-i18n.js — passed
• bunx vitest run — 1150 passed, 3 skipped

Coupling

This is the renderer half of a cross-repo fix. The backend half adds the include_disabled
query parameter to GET /api/agents and lives in iOfficeAI/AionCore#467. Both PRs are
coupled — this change only works against an AionUi build whose bundled aioncore binary
includes that backend change, so the AionCore half must be bundled for the fix to function
in a release.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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