feat(canary): webbug generator (Generate + Trigger)
- Generate returns KindURL artifact: baseURL/c/{id} (trailing slash trimmed)
- Trigger builds event from CF-Connecting-IP|XFF(rightmost)|XRI|RemoteAddr precedence,
captures UA + Referer (nil when absent), returns 43-byte GIF response with
no-store cache headers
- Nil-token path still returns GIF (spec §8.5 defense-in-depth)
- Tests: artifact shape, request metadata capture, IP precedence chain (5 cases),
nil-pointer mapping for absent headers, GIF response shape + cache headers,
missing-token path
realIP() lives here temporarily; promotes to middleware in Phase 9.
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