feat: respect server rate-limit headers and surface quota in UI

[martoniel]

Closes #842

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• Add parseRateLimitHeaders() to stellar.ts: parses X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, and Retry-After from every HTTP response into a typed RateLimitQuota snapshot. Missing or non-numeric header values are safely coerced to null.

• Wire _updateQuotaFromResponse() into rateLimitedFetch so both the immediate and queued code paths push the latest quota to the store after every response, including 429s.

• Add RateLimitQuota interface and rateLimitQuota / setRateLimitQuota slice to the Zustand store (store.ts). Starts null; updated on every API response that carries rate-limit headers.

• Add RateLimitQuotaDisplay component: shows remaining/limit counts, an accessible progress bar (green/amber/red), reset time, and a rate-limited warning state. Renders nothing until the first quota snapshot arrives.

• Add rateLimitHeaders.test.ts (15 tests): primary flow, boundary case (429 with Retry-After only), failure cases (malformed/missing headers), and store integration tests. All 15 pass.

Summary

Closes #

How was this tested?

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[Manuelshub]

@martoniel Please resolve conflicts.

[martoniel]

@Manuelshub I have resolved conflicts