feat: switch from discussions to PR-based contributions

- Add PR templates for plugins, projects, themes, agents, resources
- Update contributing.md with PR-based workflow and entry templates
- Replace all 'Suggest via Discussion' links with 'Add via PR' links
- Add quick copy templates for each entry type
- Keep existing discussion links for resource entries (they link to content)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,31 @@
+## Submission Type
+
+<!-- Check one -->
+- [ ] Plugin
+- [ ] Project
+- [ ] Theme
+- [ ] Agent
+- [ ] Resource
+
+## Details
+
+**Name:** 
+**Repository:** 
+**Description:** <!-- One sentence -->
+
+## Checklist
+
+- [ ] Relevant to OpenCode
+- [ ] Repository is public and accessible
+- [ ] Actively maintained
+- [ ] Not a duplicate
+- [ ] Entry added in alphabetical order
+- [ ] Used correct collapsible format
+
+## Entry Added
+
+<!-- Paste the entry you added to README.md -->
+
+```html
+
+```