chore: add issue and PR conventions to maintenance skill

.opencode/skills/maintenance/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: maintenance
-description: Use when making ANY code change to pytrendy. Covers commit format, branch model, deprecation policy, API surface, diff conventions, remote session behaviour, and things you must not touch. Load this FIRST before any code work.
+description: Use when making ANY code change to pytrendy, creating issues, or opening PRs. Covers commit format, PR title conventions, branch model, deprecation policy, API surface, diff conventions, remote session behaviour, and things you must not touch. Load this FIRST before any code work.
 ---
 
 # Maintenance & API evolution
@@ -92,6 +92,15 @@ Segment dicts have at minimum: `direction` ('Up'/'Down'/'Flat'/'Noise'), `start`
 - `CHANGELOG.md` — generated by semantic-release on `main`.
 - `docs/whats-new.md` — generated by the agentic `whats-new.yaml` workflow (OpenCode CLI writes between `<!-- WHATS_NEW_CONTENT_START/END -->` sentinels). Don't edit by hand unless explicitly directed to fix/regenerate an entry — the workflow overwrites content between the sentinels on the next release.
 
+## Issues and PRs
+
+When creating issues or PRs, follow the conventions in `docs/contributing.md`:
+
+- **Issue titles** use `[Tag] Short description` format: `[Bug]`, `[Docs]`, `[Enhancement]`, `[Feature]`, `[CI]`, `[Maintenance]`
+- **PR titles** follow Conventional Commits: `feat: ...`, `fix: ...`, etc. (same as commit messages)
+- **Link issues** in PR descriptions with `Closes #<number>`
+- **Labels** apply appropriate labels: `bug`, `documentation`, `enhancement`, `feature`, `test`, `maintenance`, `good first issue`, `priority`
+
 ## Remote session behaviour
 
 **Detecting CI environment:** When `PYTRENDY_CI=true` is set, you are running in a GitHub Actions environment, not a local interactive session.