docs: include coverage and provider-triad gates in the PR checklist

[2160039878-cyber]

Description

The PR template omits two requirements already enforced by CONTRIBUTING.md. Add explicit Checklist reminders for the 100% line-coverage gate and for updating matching provider code, documentation, and integration tests together.

Type of Change

• Documentation update

Related Issue

Closes #683

Changes Made

• Name the required coverage gate and its test:coverage / coverage:check commands.
• Make the provider-triad reminder conditional on changes under src/lib/db/providers/, naming docs/providers/ and tests/integration/db/ in the same PR.

Testing

Verified the checklist against CONTRIBUTING.md and reviewed the diff. Full Linux validation used the repository's unchanged CI workflow on commit ff9874b032879ccb5bfcb333e9d44943e790ed2e: run and logs.

• All 391 core test files and 34 component isolation groups passed via bun run test:coverage.
• bun run coverage:check: 46,324 / 46,324 lines (100%).
• Format, lint, typecheck, knip, README/chart/channel/security drift guards, application build, library build, and package type-resolution checks passed.
• Helm lint and the Go launcher checks passed.
• Browser E2E: 65 passed; subpath E2E: 1 passed; PostgreSQL functional smoke: 1 passed; packaged tarball and npx E2E: 3 passed each; Node 24/26 engine smoke passed.
• Secret Scan, Dependency Scan, and Image Scan passed. The manual secret scan includes all fetched fork history and branches.

The CI run's overall status is red solely because SonarCloud Analysis cannot authenticate from this fork (SONAR_TOKEN / project access unavailable). Every test/build job listed above passed. CONTRIBUTING.md and CLAUDE.md identify CI as the merge gate, and CLAUDE.md explicitly excludes SonarCloud from required checks; the upstream workflow also skips SonarCloud for fork PRs. Upstream required workflows still need their normal maintainer approval.

Full validation ran on GitHub-hosted Linux because this Windows host's Docker Desktop fails at inference-manager initialization and its native component runner encounters SQLite cleanup EBUSY. No full native-Windows pass is claimed.

Checklist

• Both issue acceptance criteria are present under Checklist.
• The wording matches the contribution guide.
• Full tests and the 100% line-coverage gate passed on the submitted commit.
• Diff reviewed; provider triad does not apply to this template-only change.

Additional Notes

AI-assisted implementation, review, and validation. This branch starts independently from main and contains only the PR-template change.

CI follow-up

The fork-run SonarCloud 401 is tracked in #732 and fixed by #733. The inherited condition admitted fork-owned pushes and fork-local PRs to the canonical SonarCloud project. The dedicated CI fix run now succeeds: all nine executable test/build jobs pass, and SonarCloud is scoped to the canonical repository. That run tests CI fix commit 80a318b; this PR's exact-head verification remains the original run linked above, whose nine executable jobs passed. Upstream Actions still await maintainer approval.

[cevheri]

Checked against #683. Both lines are there and both are accurate: the coverage gate is exactly what scripts/check-coverage.mjs enforces in the required test job, and the triad wording matches the rule as CLAUDE.md states it. That precision is the part that matters in a template, since every future contributor reads it. No test guards this file, and the only other change is one trailing blank line, so the diff stays where it should.

One wording note, not blocking. The coverage item reads "The required CI test job passes...", so its subject is CI, while the point of the issue is for a contributor to catch this before opening the PR, and the other seven items are all written from their side. Something like "I ran bun run test:coverage && bun run coverage:check and line coverage is 100%" would put it in the same voice. The commands you already put in parentheses carry the meaning either way.

Merging shortly.