wip: P1 feature batch — retry, search, code symbols, diff/status/test commands, tool output head+tail

- retry logic for transient LLM errors (openai.go)
- file_search context_lines + max_results (file.go)
- FormatResult now preserves head+tail with omitted bytes (tools.go)
- /status /diff /test slash commands wired (workflow.go, app.go)
- CodeSymbolsTool for Go package/type/func listing (code.go)
- README updated with v0.0.4 features

internal/llm/openai_test.go

@@ -66,6 +66,37 @@ func TestOpenAICompatibleClientStreamsContentAndToolCalls(t *testing.T) {
 	}
 }
 
+func TestOpenAICompatibleClientRetriesTransientHTTPError(t *testing.T) {
+	attempts := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		attempts++
+		if attempts == 1 {
+			http.Error(w, "temporary", http.StatusBadGateway)
+			return
+		}
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(`data: {"choices":[{"delta":{"content":"ok"},"finish_reason":""}]}` + "\n\n"))
+		_, _ = w.Write([]byte("data: [DONE]\n\n"))
+	}))
+	defer server.Close()
+
+	client := NewOpenAICompatibleClient(server.URL, "sk-test", server.Client())
+	var content strings.Builder
+	err := client.ChatStream(context.Background(), ChatRequest{Model: "test"}, func(event StreamEvent) error {
+		content.WriteString(event.Content)
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if attempts != 2 {
+		t.Fatalf("attempts = %d, want 2", attempts)
+	}
+	if content.String() != "ok" {
+		t.Fatalf("content = %q", content.String())
+	}
+}
+
 func mustReadBody(t *testing.T, r *http.Request) string {
 	t.Helper()
 	data, err := io.ReadAll(r.Body)