feat: retry op read with exponential backoff for flaky wifi

[smartwatermelon]

Summary

• Replaces single-timeout op read with retry loop using 2s/4s/8s exponential backoff
• Fast connections succeed on first attempt unchanged; flaky wifi gets 3 chances across ~14s
• Fixes intermittent could not retrieve GH_TOKEN warnings on slow networks

Test plan

• shellcheck passes
• All 59 tests pass
• Both code-reviewer and adversarial-reviewer PASS (2 commits)
• Manual: verify with CLAUDE_DEBUG=true claude on slow wifi — debug log should show retry attempts
• Manual: verify fast wifi still resolves on first attempt with no delay

🤖 Generated with Claude Code

[claude]

The change adds a retry loop with increasing timeouts (2s → 4s → 8s) for op read in _load_gh_token(). No BLOCK criteria met:

• Logic is correct: if "${has_timeout}" is valid bash (evaluates true/false as commands).
• No silent failure path: the existing post-loop token check still handles all retries exhausted.
• No security regression: credentials handling is unchanged.

VERDICT: PASS