feat: add operator AI kill switch

[Gojv-byte]

Summary

Adds a server-controlled global kill switch for experimental AI panels. Operators can disable or re-enable panels without redeploying. Production uses shared Redis; AI panels fail closed when status is unavailable.

Closes #830

How was this tested?

• corepack pnpm exec vitest run --config vitest.config.js tests/api/aiKillSwitch.test.js src/lib/__tests__/featureFlagLifecycle.test.ts — 12 tests passed. Covers updating the switch and audit history, invalid input, unauthorized operators, unsupported environments, and unavailable storage.
• corepack pnpm run build and the bundle-budget check passed.
• Targeted lint and formatting checks passed.

Merge requirements

A PR is merged only when every box below is true. See
Merge requirements for the full policy.

• All required CI checks pass on the latest commit (not just an earlier push).
• No required checks are failing, pending, or skipped — re-run or fix them; do not ask for a merge while any are outstanding.
• The branch has no merge conflicts with the target branch (rebase or merge master if GitHub shows "This branch has conflicts").
• Tests were added or updated for the change (primary flow, a boundary case, and a failure case).
• Docs were updated where behaviour, configuration, or security posture changed.

Security-sensitive changes

• This PR touches a path covered by .github/CODEOWNERS (wallet, auth, cryptography, CI) and a code owner has been requested for review.
• I described any change to key handling, signing, session lifetime, or trusted endpoints above.
• Writes to /api/v1/ai-controls require a server-configured operator token. The token is compared in constant time, held only in browser memory, and never persisted. Production requires shared Redis; requests fail closed if runtime state is unavailable.

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