feat(github): add milestone creation/assignment to the issue-planning tool

[JSONbored]

Summary

• Adds src/github/milestones.ts (listOpenInstallationMilestones, createInstallationMilestone) — GitHub-native milestones didn't exist as a capability anywhere in this codebase before this PR; every prior milestone reference was either the read-only milestoned/demilestoned webhook event or an unrelated Linear-integration field. Both new functions go through the same installation-token/Orb-broker path as issue creation (#7425) — never a flat PAT.
• Extends loopover_plan_repo_issues (#7426) with an optional milestone target (title/description/dueOn, all maintainer-supplied — never model-generated, per this sub-issue's own boundary). When creating ({create:true, dryRun:false}), the milestone is resolved once for the whole batch, then assigned to every issue actually created.
• Reuse heuristic: an exact normalized-title match (reusing normalizeIssueTitleKey, already generic) against existing open milestones — deliberately not fuzzy. A fuzzy match risks silently grouping issues under the wrong milestone, which is worse than creating a new, differently-named one. This mirrors the manual convention .claude/skills/contributor-pipeline-gardening already follows (reusing one milestone across recurring rounds) instead of spawning a fresh one every planning run under the same title.
• Milestone resolution degrades gracefully on any failure (a GitHub error, a suppressed/malformed create): the maintainer still gets their issues, just ungrouped (milestoneNumber absent in the result), rather than the whole batch failing over a milestone-specific glitch.
• A dry-run preview makes no milestone-related GitHub calls at all, even when a milestone target is supplied — consistent with the tool's existing "nothing is written until {create:true, dryRun:false}" contract.
• Sub-issue of #7424 (Epic: ORB self-hoster issue & milestone planning routine).

Scope

• The PR title follows type(scope): short summary Conventional Commit format, for example fix(api): restore profile access checks.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• I linked a currently open issue this PR resolves (e.g. Closes #123) — a linked open issue is required for every contributor PR.

Validation

• git diff --check
• npm run typecheck
• npm run test:coverage locally — full unsharded suite: 1021 files / 19386 tests passed, 2 skipped. The same 9 pre-existing failures in 3 unrelated miner test files (tracked separately, unrelated to this PR) reproduce identically regardless of this change. New/changed code (src/github/milestones.ts, the milestone additions to src/services/issue-plan-draft.ts, the MCP wiring) is 100% branch-covered.
• npm run build:mcp / npm run test:mcp-pack
• npm run selfhost:env-reference:check / npm run ui:openapi:check / npm run docs:drift-check / npm run manifest:drift-check — all clean; no new env vars, no OpenAPI/manifest surface touched (MCP-only).
• npm run ui:lint / npm run ui:typecheck / npm run ui:build / npm run test:workers — not run; this PR touches no files under apps/loopover-ui/** or Cloudflare-workers-pool-specific code.
• New or changed behavior has unit/integration tests for new branches, fallback paths, and sanitizer boundaries — test/unit/github-milestones.test.ts (7 tests, 100% branch coverage), milestone-specific additions to test/unit/issue-plan-draft.test.ts (6 new tests: no-op on dry run, create-new, reuse-by-normalized-title, empty-normalized-title, degrade-on-failure, no-installation) and test/unit/mcp-plan-repo-issues.test.ts (milestone round-trip).

If any required check was skipped, explain why:

• ui:lint/ui:typecheck/ui:build/test:workers: no apps/loopover-ui/** or workers-pool-specific files changed.

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed.
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics.
• Auth, cookie, CORS, GitHub App, Cloudflare, or session changes include negative-path tests — non-2xx GitHub response, suppressed non-live mode, malformed response, missing installation, and milestone-resolution failure are all covered.
• API/OpenAPI/MCP behavior is updated and tested where needed — MCP schema/tool extension fully tested; no HTTP/OpenAPI surface added.
• UI changes use live API data or real empty/error/loading states. (N/A — no UI.)
• Visible UI changes include a UI Evidence section. (N/A — backend/MCP-only change.)
• Public docs/changelogs are updated where needed. (N/A — no user-facing docs surface beyond the tool's own description string, included in this diff.)

UI Evidence

N/A — this is a backend/MCP-only change with no visible UI, frontend, or docs surface.

Notes

• Sub-issue of #7424. Extends #7426's loopover_plan_repo_issues tool (already merged, #7476), built on #7425's installation-token/Orb-broker write path (already merged, #7467).

Closes #7427

[superagent-security]

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.42%. Comparing base (98a8371) to head (20b5f7e).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7511      +/-   ##
==========================================
- Coverage   91.43%   91.42%   -0.02%     
==========================================
  Files         718      719       +1     
  Lines       73214    73253      +39     
  Branches    21692    21701       +9     
==========================================
+ Hits        66944    66972      +28     
- Misses       5227     5234       +7     
- Partials     1043     1047       +4     

Flag	Coverage Δ
shard-1	32.84% <2.38%> (+6.65%)	⬆️
shard-2	34.13% <2.38%> (-3.20%)	⬇️
shard-3	30.50% <100.00%> (-5.87%)	⬇️
shard-4	44.95% <2.38%> (+2.03%)	⬆️
shard-5	36.03% <2.38%> (-2.16%)	⬇️
shard-6	36.19% <2.38%> (+2.49%)	⬆️

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

Files with missing lines	Coverage Δ
src/github/issues.ts	100.00% <100.00%> (ø)
src/github/milestones.ts	100.00% <100.00%> (ø)
src/mcp/server.ts	96.45% <100.00%> (+<0.01%)	⬆️
src/services/issue-plan-draft.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes