feat(results): signal auto-merged remote pushes

[christso]

Summary

• Hard-deprecate results.sync.push_conflict_policy: backup_and_force_push: it only shipped on the npm next tag, so the supported schema now accepts only block and rejects the removed value with migration guidance.
• Drop the removed value from project registry parsing on load so old local registry config rewrites to the supported shape on next save.
• Add an auto_merged_remote wire signal that is set only when resolveResultBranchPushConflict takes the diverged 3-way auto-merge path.
• Plumb the signal through direct-push result aggregation, Dashboard types, sync feedback, and docs so the Dashboard success feedback includes Merged remote (auto).
• Document the release-channel learning in docs/solutions/conventions/ and add release-channel vocabulary to CONCEPTS.md.

Validation

• bun test packages/core/test/evaluation/results-repo.test.ts
• bun test packages/core/test/evaluation/loaders/config-loader.test.ts packages/core/test/projects.test.ts packages/core/test/evaluation/validation/config-validator.test.ts
• bun test apps/dashboard/src/lib/project-sync-status.test.ts
• bun run typecheck
• bun run lint

Review

Draft PR for review before squash merge. Do not merge without a human review and passing GitHub Actions.

Tracks av-raf.5.

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