fix(server): raise storyboard eval/step rate limits for member dev iteration

[bokelley]

Closes #3277

Storyboard eval rate limits were too tight for member developer iteration: 5 evals/hr = roughly 2 debug cycles before hitting the wall on a single agent. This PR implements Option B from the issue (the author's recommendation): raise the caps to match a realistic iteration cadence.

Changes:

• storyboardEvalRateLimiter: max 5 → 10/hr
• storyboardStepRateLimiter: max 30 → 60/hr
• Both 429 handlers: fix retryAfter to use the real window-position value from the Retry-After header via parseRetryAfterSeconds (was hardcoded Math.ceil(60 * 60) = always 3600s regardless of elapsed time). Pattern matches agentReadRateLimiter in the same file.
• Error message strings updated to reflect new limits

Non-breaking justification: server-side config change only; no protocol schema, task definition, or API contract changes. Admin bypass (skipForAdmins) and skipFailedRequests: true behavior unchanged.

Option A (per-agent keying) deferred: the issue author recommends "only do A if non-admin reports keep coming." Option A also has an open design question (multiply-vs-fixed ceiling) and the correct key source is req.params.encodedUrl not req.body.agent_url — needs owner input before implementation.

Pre-PR review:

• code-reviewer: approved — one blocker (missing changeset) fixed; retryAfter pattern is correct; no new security surface
• internal-tools-strategist: approved — standardHeaders: true sets the Retry-After header before the handler fires so res.getHeader('Retry-After') is always available; window-transition behavior (users at 5/5 before deploy get 5 more in-place) is intentional

Triage-managed PR. This bot does not currently iterate on
review comments or PR conversation threads (only on the source
issue). To unblock:

• Push fixup commits directly: gh pr checkout <num> →
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  issue.

See #3121
for context.

Session: https://claude.ai/code/session_01SPJGvJCxD961HSCvtwyj3D

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[bokelley]

claude-triaged

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