feat(code reviewer) Begin deprecation of code review custom instructions

[St0rmz1]

Summary

Starts deprecating the code reviewer's Custom Instructions field in favor of REVIEW.md. The field no longer renders for configs that have never used it. Configs that already have a value keep the field, with a note pointing them to REVIEW.md.

UI only. The schema, tRPC routers, and prompt generation are untouched, so stored custom instructions are still saved and still applied to reviews.

Changes

• ReviewConfigForm.tsx (GitHub and GitLab, org and personal scopes): gate the Custom Instructions block behind new showCustomInstructions state, set on config load when the stored value is non-empty. The old helper text ("Add specific guidelines for your team's code review standards") is replaced by the deprecation note plus a link to the existing REVIEW.md guide page.
• BitbucketReviewConfigForm.tsx: same gating and note for Bitbucket's separate custom instructions field, which had no helper text before.
• platform-overview-rows.ts (mobile): drop the Custom Instructions row from the provider overview when nothing is stored, which also removes the only route to the edit screen. The subtitle is now always "Set", since the row only renders when a value exists.
• instructions.tsx (mobile edit screen): same note above the input.

Wording is identical on all three surfaces:

Custom Instructions is planned for deprecation. Move these guidelines into a REVIEW.md file in your repository instead.

Verification

• No manual testing yet. Checked with pnpm --filter web typecheck, pnpm lint in apps/mobile, and oxfmt. The conditional rendering still needs a pass against one config with a stored value and one without.

Visual Changes

Before	After

Reviewer Notes

• Visibility is sticky per page load. If someone clears the box and saves, the section stays visible until reload so it does not vanish mid-edit. A fresh load then hides it.
• The Bitbucket note links to the org-scoped guide path directly, since Bitbucket config is org only. The shared form reuses its existing reviewMdGuideHref, which already covers both scopes.
• Mobile has no REVIEW.md guide route, so the note there carries no link.
• Not in this PR, but worth knowing: the REVIEW.md guide page these notes link to still lists "Custom instructions and focus areas are still applied around repository guidance" as a limitation (ReviewMdGuideContent.tsx:30). That reads oddly as the destination of a deprecation notice.
• "planned for deprecation" is deliberately vague on timing because there is no target date set.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Reviewed the deprecation of the Custom Instructions field across web and mobile config forms; the show-once-set gating logic and REVIEW.md links are consistent and no bugs were found in the changed lines.

Files Reviewed (4 files)

• apps/mobile/src/app/(app)/(tabs)/(3_profile)/code-reviewer/[scope]/[platform]/(edit)/instructions.tsx
• apps/mobile/src/components/code-reviewer/platform-overview-rows.ts
• apps/web/src/components/code-reviews/BitbucketReviewConfigForm.tsx
• apps/web/src/components/code-reviews/ReviewConfigForm.tsx

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_{Reviewed by claude-sonnet-5 · Input: 18 · Output: 3.2K · Cached: 431.3K}

_{Review guidance: REVIEW.md from base branch main}