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/service/semantic_search_test.go

@@ -0,0 +1,143 @@
+package service
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestSemanticSearchService_Search(t *testing.T) {
+	// Mock Ollama server
+	ollamaServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/embeddings" {
+			t.Errorf("expected /api/embeddings, got %s", r.URL.Path)
+		}
+		var req ollamaEmbedRequest
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			t.Fatalf("failed to decode request: %v", err)
+		}
+		if req.Model != "nomic-embed-text" {
+			t.Errorf("expected model nomic-embed-text, got %s", req.Model)
+		}
+		if req.Prompt == "" {
+			t.Error("expected non-empty prompt")
+		}
+		// Return a 768-dim embedding (truncated for test)
+		embedding := make([]float64, 768)
+		embedding[0] = 0.1
+		embedding[1] = -0.2
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(ollamaEmbedResponse{Embedding: embedding})
+	}))
+	defer ollamaServer.Close()
+
+	// Mock Qdrant server
+	qdrantServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/collections/media/points/search" {
+			t.Errorf("expected /collections/media/points/search, got %s", r.URL.Path)
+		}
+		var req qdrantSearchRequest
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			t.Fatalf("failed to decode request: %v", err)
+		}
+		if req.Limit != 5 {
+			t.Errorf("expected limit 5, got %d", req.Limit)
+		}
+		if !req.WithPayload {
+			t.Error("expected WithPayload=true")
+		}
+		payload, _ := json.Marshal(qdrantPayload{
+			ID:        42,
+			Title:     "Blade Runner 2049",
+			MediaType: "movie",
+			Year:      intPtr(2017),
+			Overview:  "A young blade runner's discovery of a long-buried secret leads him to track down former blade runner Rick Deckard.",
+		})
+		resp := qdrantSearchResponse{
+			Result: []qdrantHit{
+				{ID: "42", Score: 0.8712, Payload: payload},
+			},
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer qdrantServer.Close()
+
+	svc := NewSemanticSearchService(ollamaServer.URL, qdrantServer.URL)
+	results, err := svc.Search(context.Background(), "sci-fi noir film", 5)
+	if err != nil {
+		t.Fatalf("Search failed: %v", err)
+	}
+
+	if len(results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(results))
+	}
+	if results[0].ID != 42 {
+		t.Errorf("expected ID 42, got %d", results[0].ID)
+	}
+	if results[0].Title != "Blade Runner 2049" {
+		t.Errorf("expected title 'Blade Runner 2049', got %s", results[0].Title)
+	}
+	if results[0].MediaType != "movie" {
+		t.Errorf("expected media_type 'movie', got %s", results[0].MediaType)
+	}
+	if results[0].Score != 0.8712 {
+		t.Errorf("expected score 0.8712, got %f", results[0].Score)
+	}
+	if results[0].Year == nil || *results[0].Year != 2017 {
+		t.Error("expected year 2017")
+	}
+}
+
+// Note: empty query validation happens at the API handler level (search.go),
+// not in the service. The service layer trusts its callers.
+func TestSemanticSearchService_embed_emptyQuery(t *testing.T) {
+	ollamaServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Empty string is passed through to Ollama — Ollama may return an error
+		w.WriteHeader(http.StatusBadRequest)
+	}))
+	defer ollamaServer.Close()
+
+	svc := NewSemanticSearchService(ollamaServer.URL, "http://localhost:6333")
+	_, err := svc.embed(context.Background(), "")
+	if err == nil {
+		t.Error("expected error for empty query passed to Ollama")
+	}
+}
+
+func TestSemanticSearchService_qdrantError(t *testing.T) {
+	ollamaServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		embedding := make([]float64, 768)
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(ollamaEmbedResponse{Embedding: embedding})
+	}))
+	defer ollamaServer.Close()
+
+	qdrantServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusServiceUnavailable)
+	}))
+	defer qdrantServer.Close()
+
+	svc := NewSemanticSearchService(ollamaServer.URL, qdrantServer.URL)
+	_, err := svc.Search(context.Background(), "test query", 5)
+	if err == nil {
+		t.Fatal("expected error when Qdrant is unavailable")
+	}
+}
+
+func TestSemanticSearchService_ollamaError(t *testing.T) {
+	ollamaServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusServiceUnavailable)
+	}))
+	defer ollamaServer.Close()
+
+	svc := NewSemanticSearchService(ollamaServer.URL, "http://localhost:6333")
+	_, err := svc.Search(context.Background(), "test query", 5)
+	if err == nil {
+		t.Fatal("expected error when Ollama is unavailable")
+	}
+}
+
+func intPtr(i int) *int { return &i }