P1: GitHub API hardening (token support, retries, rate-limit messaging)

[Kinin-Code-Offical]

[Kinin-Code-Offical]

Plan:

• Add GitHub API request helper with retries and optional token header.
• Surface rate-limit errors with reset time when remaining=0.
• Wire helper into release lookup endpoints.

Risks:

• Incorrect retry handling could mask real errors; keep limited retries.

Tests:

• npm ci
• npm run lint
• npm test
• npm run build

[Kinin-Code-Offical]

PR merged: #37
Merge commit: 72bc82e