fix: recover retryable reviewer timeouts

[mrcfps]

Summary

• Recover failed reviewer loops whose latest queue failure is retryable_transient while queue attempts remain.
• Preserve the queue attempt count when requeueing these stranded retryable failures so recovery does not expand the configured retry budget.
• Add reviewer, runtime, and storage coverage for retryable transient recovery and attempt preservation.

Validation

• go test ./internal/reviewer ./internal/runtime ./internal/storage
• GOCACHE=/tmp/looper-go-cache go test ./internal/agent
• GOCACHE=/tmp/looper-go-cache go vet ./...
• GOCACHE=/tmp/looper-go-cache go build ./...

GOCACHE=/tmp/looper-go-cache go test ./... was attempted, but this sandbox blocks local httptest port binding and reports the default ~/.looper/worktrees path as non-writable in config tests.

Closes #221

_{Generated by Looper 0.6.0 · runner=worker · agent=codex}

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[mrcfps]

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[chatgpt-codex-connector]

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Reviewed commit: c57f00927f

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