fix(helpers): make X-AIMock-Strict header parsing case-insensitive and whitespace-tolerant

[Ayush7614]

Clients, proxies, and shell snippets often emit X-AIMock-Strict: True, TRUE, or true with surrounding whitespace. The previous resolveStrictMode compared literally against "true"/"false"/"1"/"0", so those variants silently fell back to the server default.

On a --strict false server that meant X-AIMock-Strict: True stayed at 404 instead of 503; on a --strict true server X-AIMock-Strict: False stayed strict. The same header also gates reasoning suppression, so the mismatch could surface as flaky reasoning assertions.

Change:

• Trim surrounding whitespace and lower-case the header value before comparing
• "true"/"TRUE"/" True " / "1" / " 1 " → strict on
• "false"/"FALSE"/" false " / "0" / " 0 " → strict off
• Unrecognised values still fall back to serverDefault

Verified:

• pnpm run format:check / lint / typecheck clean
• Manual probe via createServer:

  strict:false + True/TRUE/" TRUE "/1 → 503 (was 404 before on capitalised variants)
  strict:true  + False/FALSE/" FALSE "/0 → 404 (was 503 before)
  unknown "maybe" → falls back to server default
  

• Existing openrouter-video.test.ts strict-header tests (lower-case) still pass (123 passed)