fix: group pool connections and clarify routing controls

[ctkm-aelf]

Summary

• Group the searchable connection selector by original catalog service, with individual accounts/keys expanded beneath each heading. Keep different catalog identities separate even when their names match, and search original service names/slugs before pagination without broadening access.
• Expose routing controls in the main form: move weighted and round-robin members, show cycle positions and configured weighted shares, and adjust fallback priorities and same-priority balancing. A weighted A(2), B(1) cycle is A → A → B; reordering gives B → A → A. Saving retains the current routing counter.
• Fix the fresh-dialog Routing dropdown's ResizeObserver race and keep the picker usable in short/mobile viewports. Preserve the earlier unavailable-credential API correction, selection across searches, and saved member settings.

Test Plan

• Full frontend suite: 4,118 tests in 412 files; 30 focused pool tests.
• Frontend lint (no errors or new warnings) and production build.
• Three permanent Playwright regressions against the production build: grouped selection, fresh Routing dialogs, and short viewports with a complete row fitting inside the scroll area.
• Independent real API/CLI/browser acceptance: 20 checks covering create/edit/reopen/delete, original-service grouping/search, actual weighted/round-robin/priority dispatch, disabled members, retained cycle position, and the earlier HTTP 400 contract.
• Independent browser checks: 30 fresh Routing dialogs and seven viewport sizes, with zero window/page/console errors.
• Extended MongoDB 8 inspection regression: literal case-insensitive original-name/slug search before pagination, owner/service scopes, and no credential materialization.
• Rust formatting and backend architecture boundary check.
• Workspace Clippy in CI and AWS, GCP, and combined KMS feature builds.
• Rebased CLI pool command and boundary tests: 31 passed.
• Full backend CI passed on final head 9e7a402d, including the fix: settled pool attempts are never lease-lost; terminate hung tests after five minutes in CI #1739 runtime fix. Local MongoDB 8 rerun also passed every case affected by an earlier Mongo diagnostic-file crash, including all candidate-inspection cases; final-head CI supersedes the interrupted broader local run.
• Final-head CI Pipeline, backend/frontend coverage, billing smoke, production backend build, all KMS builds, and all CodeQL analyses passed. GitHub reports no merge conflicts.

Checklist

• Code follows the project's architecture rules.
• No hardcoded secrets or credentials.
• Error messages do not leak internal details.
• API, service pool, and validation documentation updated.

Rebased onto latest main (ef830db7), including the settled-attempt lease correction in #1739. Follow-up to #1732 and #1680.

Merge status: ready for review. Normal squash merge was attempted and blocked by the main-branch ruleset requiring one approving review. No approval has been submitted; repository auto-merge is disabled.

[github-actions]

📊 Code coverage

Component	Lines	Threshold	Status	Δ vs base
Backend (nyxid)	87.58%	73%	✅	— 0.00
Frontend (vitest)	71.94%	15%	✅	🔺 +0.04

Gate: line coverage must stay at or above the threshold. Ratchet plan (W21): Backend → 55%, CLI → 50%, Frontend → 30% by quarter end.