refactor(code-review): remove feature flags

[alex-alecu]

Summary

• Run the GitHub and GitLab merge-commit skip check before cancelling in-flight reviews, and add handler tests so "Update branch" or rebase merge commits do not leave a PR or MR without an active review.
• Remove the three code review feature flags so new reviews always dispatch as v2, always include PR gate behavior, and always reuse the last completed review for continuation when available.
• Simplify the personal and organization review config responses plus the settings form by dropping flag-derived UI fields while keeping existing agent_version, v1 event streaming, and admin reporting paths unchanged.

Verification

• Not run manually; reproducing these webhook-driven review flows requires GitHub or GitLab events, so I validated the branch with local automated checks instead.

Visual Changes

N/A (small settings-form visibility change only; no screenshots captured)

Reviewer Notes

• The final PR scope is intentionally limited to two commits: the merge-commit cancellation fix and the review-flag removal. The earlier broader refactor was reset away before this diff was rebuilt.
• agent_version storage/admin views and the legacy v1 streaming/event paths are intentionally still present; this PR only removes the feature-flag gates around them.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• apps/web/src/lib/code-reviews/db/code-reviews.ts
• apps/web/src/lib/code-reviews/db/code-reviews.test.ts

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_{Reviewed by gpt-5.4-20260305 · 812,131 tokens}

[alex-alecu]

Manual test passed.

Tested:

• GitLab merge_request.update webhook replay with a two-parent merge-commit head through the local Next.js webhook route.
• GitLab merge_request.update webhook replay with a normal one-parent head through commit-status, reaction, payload preparation, and review-worker dispatch paths.

Verified:

• Merge commit returned 200 with "Skipped merge commit", persisted a processed webhook event, created no review row for the merge SHA, and preserved the pre-existing active review.
• Normal commit returned 202 with "Code review queued" and persisted exactly one new GitLab review row with agent_version = v2.
• Dispatch payload included agentVersion = v2, gateThreshold = warning, and the configured thinking-effort variant, and GitLab side effects were requested for pending commit status, eyes reaction, and superseded-review cancellation.