refactor(rate-limit): 1 req/sec cooldown, batch up to 2048 (#3)

* refactor(rate-limit): switch to 1 req/sec cooldown, batch size up to 2048

Replace per-pixel credit/token-bucket model with a simple per-user cooldown
(SET NX EX 1). Batch size is now independent of the rate limit and capped
at MAX_BATCH_SIZE = 2048.

- rate-limiter: SET NX EX replaces Lua credit script
- worker: response shape { ok: true } (no credits field)
- client: drop credit state/timer/UserInfo; uploader paces by cooldown
- tests: mock checkRateLimit; integration test exercises SET NX EX
- docs: README, system-architecture, code-standards, deployment-guide

* chore(plans): remove implemented plan directories

rplace-implementation (base build), review-fixes, and
image-importer-enhancements are all shipped. Keep plans/reports/ as
historical code-review and research references.

docs/code-standards.md

@@ -46,5 +46,5 @@ src/
 
 ## API Response Format
 
-Success: `{ ok: true, credits: N }`
-Error: `{ error: "error_code", ...details }` with appropriate HTTP status
+Success: `{ ok: true }`
+Error: `{ error: "error_code", ...details }` with appropriate HTTP status (e.g., `retryAfter` on 429)