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

internal/api/search.go

@@ -54,6 +54,35 @@ func searchReleases(svc *service.SearchService) echo.HandlerFunc {
 	}
 }
 
+func semanticSearch(svc *service.SemanticSearchService) echo.HandlerFunc {
+	return func(c echo.Context) error {
+		ctx, cancel := context.WithTimeout(c.Request().Context(), 30*time.Second)
+		defer cancel()
+
+		query := c.QueryParam("q")
+		if query == "" {
+			return c.JSON(http.StatusBadRequest, map[string]string{"error": "q parameter is required"})
+		}
+
+		k := 5
+		if kStr := c.QueryParam("k"); kStr != "" {
+			if kVal, err := strconv.Atoi(kStr); err == nil && kVal > 0 && kVal <= 50 {
+				k = kVal
+			}
+		}
+
+		results, err := svc.Search(ctx, query, k)
+		if err != nil {
+			slog.Error("semantic search failed", "error", err)
+			return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+		}
+
+		return c.JSON(http.StatusOK, map[string]interface{}{
+			"results": results,
+		})
+	}
+}
+
 func grabRelease(svc *service.SearchService, dcSvc *service.DownloadClientService, queueSvc *service.QueueService, safetySvc *service.SafetyService, activitySvc *service.ActivityService) echo.HandlerFunc {
 	return func(c echo.Context) error {
 		ctx, cancel := context.WithTimeout(c.Request().Context(), 30*time.Second)