fix: retry transient HTTP failures

[victor0602]

What changed

• Add centralized, bounded retries for transient network failures and HTTP 408, 429, 500, 502, 503, and 504 responses.
• Use exponential backoff with jitter, honor Retry-After, and cap delays.
• Recreate per-attempt timeout signals and safely replay JSON and FormData request bodies.
• Keep permanent HTTP errors fail-fast.

Why

The shared HTTP layer previously made a single attempt, exposing every command and SDK operation to temporary rate limits, service errors, and network instability.

Impact

Transient failures can recover automatically while retry counts and delays remain bounded.

Checks

• bun test — 469 passed
• bun run typecheck
• bun run lint — no errors; one pre-existing test warning
• git diff --check

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