docs(openapi): document validate-linked-issue + check-before-start routes (#9304)

[RealDiligent]

Problem

Closes #9304.

Two live POST /v1/repos/:owner/:repo/* pre-work-check routes in src/api/routes.ts each already have an MCP tool with its own Zod shapes in src/mcp/server.ts, but neither appears in src/openapi/spec.ts:

• POST …/validate-linked-issue → loopover_validate_linked_issue (validateLinkedIssueOutputSchema)
• POST …/check-before-start → loopover_check_before_start (checkBeforeStartOutputSchema)

Fix

Mirrors the #6611 pattern for gate-config/effective (and the evaluate-escalation POST mirror):

1. src/openapi/schemas.ts: added ValidateLinkedIssueRequestSchema/ValidateLinkedIssueResponseSchema and CheckBeforeStartRequestSchema/CheckBeforeStartResponseSchema — field-level parity with the MCP tools' inputSchema/outputSchema (following the repo convention of representing shapes with basic Zod types, without the internal PREFLIGHT_LIMITS max constraints).
2. src/openapi/spec.ts: registry.register all four as components and registerPath both routes (params + request body + response, with 400/401/403).
3. Regenerated apps/loopover-ui/public/openapi.json — committed here; npm run ui:openapi:check enforces it in CI.

Verification

test/unit/openapi.test.ts passes; buildOpenApiSpec() includes both new paths; regeneration is byte-stable (100% patch coverage on the new schemas.ts/spec.ts lines via the openapi test).

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[loopover-orb]

Important

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⏳ LoopOver is waiting…

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed · 🟨 Waiting}

[loopover-orb]

This repository reviews pull requests one-shot: the PR must be correct as originally opened. Pushing an additional commit closes it automatically instead of restarting review — open a fresh pull request with every fix included.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.69%. Comparing base (fb8e2eb) to head (75bbffd).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #9440       +/-   ##
===========================================
- Coverage   89.54%   75.69%   -13.86%     
===========================================
  Files         843      277      -566     
  Lines      110011    58466    -51545     
  Branches    26184     6216    -19968     
===========================================
- Hits        98511    44253    -54258     
- Misses      10238    13942     +3704     
+ Partials     1262      271      -991     

Flag	Coverage Δ
backend	99.76% <100.00%> (+4.50%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/openapi/schemas.ts	100.00% <100.00%> (ø)
src/openapi/spec.ts	99.62% <100.00%> (+<0.01%)	⬆️

... and 704 files with indirect coverage changes