feat: semantic search with Qdrant + Ollama embeddings

- Add SemanticSearchService with embed() + searchQdrant() methods
- Add GET /api/search/semantic endpoint (?q=query&k=5)
- Wire SemanticSearchService into router and cmd/server/main.go
- Add SemanticSearch React page with results + similarity scores
- Add 'Semantic Search' nav link in App.tsx
- Add unit tests with mocked Ollama + Qdrant HTTP servers (4 tests, all passing)
- Add GitHub issue templates (bug report, feature request)
- Add pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,28 @@
+## Description
+
+Brief summary of what this PR does.
+
+## Type of Change
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Breaking change
+- [ ] Documentation update
+
+## Testing
+
+Describe what testing you performed.
+
+- [ ] Tested locally (go test ./...)
+- [ ] Tested in Docker Compose dev environment
+- [ ] Verified frontend builds (npm run build)
+
+## Checklist
+
+- [ ] My code follows the project conventions (see AGENTS.md)
+- [ ] I have self-reviewed my own code
+- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] I have made corresponding changes to the documentation
+- [ ] My changes generate no new compiler or lint warnings
+- [ ] I have added tests that prove my fix is effective or my feature works
+- [ ] New and existing unit tests pass locally with my changes