fix(frontend): prevent duplicate datasource mutations

[openai0229]

Related issue

N/A - reported from a user reproduction video.

Summary

Prevent rapid repeated save/update actions from creating duplicate datasources. Serialize position changes per tree node, refresh the complete datasource tree after the server confirms a move, and leave the displayed tree unchanged when a move fails.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results: yarn test:data-source-mutation-refresh passed; yarn lint passed; yarn build:web:community --app_version=0.0.0 passed, including the full prebuild suite and production bundle verification; the clean-worktree Community backend package also passed with tests skipped.
• Manual verification: started the PR backend on isolated port 18825 with a temporary Community profile and the PR frontend on 8892; connected to a disposable database/user on local Docker MySQL 8.4.8; created a datasource inside a group by firing two save clicks in the same browser task and observed exactly one real create request, one ID, and one tree node; moved it group-to-root and root-to-group with persisted one-node results; simulated a 500 move response and confirmed no refresh or local position change; delayed a move response and performed two rapid drags, observing exactly one update request; reloaded and confirmed one persisted datasource node.
• UI evidence: Verified with Playwright CLI; temporary browser artifacts and test data were removed after validation.

Risk and compatibility

• Public API or stored data: No API or persistence schema changes. Existing duplicate tree data is intentionally not migrated.
• Database or driver compatibility: Database-neutral frontend behavior; manual validation used MySQL 8.4.8.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: Community shared frontend only; commercial storage implementations require separate fixes.
• Backward compatibility: Existing create and move request contracts are preserved.

Reviewer map

• Start here: src/components/ConnectionEdit/submissionGuard.ts and src/blocks/NewTree/treePositionMutation.ts.
• Failure condition: two create/update requests can run concurrently, a failed move changes local tree state, or a successful move does not refresh the server tree.
• Rollback or disable path: revert this commit; no stored-data rollback is needed.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: Codex analyzed the reproduction, implemented the frontend concurrency guards and server-authoritative refresh flow, added focused regression tests, and performed the isolated Playwright CLI regression.