fix(db): make edge rebinding atomic

[cbeaulieu-gt]

Summary

• replace resolution-edge deletion and unresolved-reference insertion inside one database transaction
• preserve the previously committed edge if requeue insertion fails
• add convergence coverage for same-target rebinding and forced rollback
• document the fix in the unreleased changelog

Verification

• npm test -- __tests__/sync-rebuild-convergence.test.ts — 10 passed
• npm run build — passed
• npm test after building — 4,329 passed, 55 failed, 227 skipped on Windows; the remaining failures are outside the changed sync code and include existing UI expectations, watcher timing, PID-1 assumptions, and worker exits. Hosted CI is the clean-platform check.

Fixes #1833

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