feat(mcp): add describe_tools and annotate_tool functionality

* Implement DescribeTool for listing available MCP tools with annotations.
* Add UpsertToolAnnotation and GetToolAnnotations methods for managing tool notes.
* Create tool_annotations table for storing tool usage notes.

internal/app/app.go

@@ -188,6 +188,7 @@ func routes(logger *slog.Logger, cfg *config.Config, info buildinfo.Info, db *st
 		CRM:           tools.NewCRMTool(db),
 		Skills:        tools.NewSkillsTool(db, activeProjects),
 		ChatHistory:   tools.NewChatHistoryTool(db, activeProjects),
+		Describe:      tools.NewDescribeTool(db, mcpserver.BuildToolCatalog()),
 	}
 
 	mcpHandler, err := mcpserver.New(cfg.MCP, logger, toolSet, activeProjects.Clear)
@@ -207,6 +208,7 @@ func routes(logger *slog.Logger, cfg *config.Config, info buildinfo.Info, db *st
 	}
 	mux.HandleFunc("/favicon.ico", serveFavicon)
 	mux.HandleFunc("/images/project.jpg", serveHomeImage)
+	mux.HandleFunc("/images/icon.png", serveIcon)
 	mux.HandleFunc("/llm", serveLLMInstructions)
 
 	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
@@ -342,3 +344,26 @@ func serveHomeImage(w http.ResponseWriter, r *http.Request) {
 
 	_, _ = w.Write(homeImage)
 }
+
+func serveIcon(w http.ResponseWriter, r *http.Request) {
+	if iconImage == nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	if r.Method != http.MethodGet && r.Method != http.MethodHead {
+		w.Header().Set("Allow", "GET, HEAD")
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	w.Header().Set("Content-Type", "image/png")
+	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
+	w.WriteHeader(http.StatusOK)
+
+	if r.Method == http.MethodHead {
+		return
+	}
+
+	_, _ = w.Write(iconImage)
+}