style: fix all golangci-lint issues and format code (refs #17)

Fix 380 lint violations across all Go source files including wsl_v5,
nlreturn, noinlineerr, errcheck, funlen, funcorder, tagliatelle,
perfsprint, modernize, revive, gosec, ireturn, mnd, forcetypeassert,
cyclop, and others.

Key changes:
- Split large handler/command functions into smaller methods
- Extract scan helpers for database queries
- Reorder exported/unexported methods per funcorder
- Add sentinel errors in models package
- Use camelCase JSON tags per tagliatelle defaults
- Add package comments
- Fix .gitignore to not exclude cmd/chat-cli directory

internal/server/routes.go

@@ -71,17 +71,37 @@ func (s *Server) SetupRoutes() {
 		s.log.Error("failed to get web dist filesystem", "error", err)
 	} else {
 		fileServer := http.FileServer(http.FS(distFS))
+
 		s.router.Get("/*", func(w http.ResponseWriter, r *http.Request) {
-			// Try to serve the file; if not found, serve index.html for SPA routing
-			f, err := distFS.(fs.ReadFileFS).ReadFile(r.URL.Path[1:])
-			if err != nil || len(f) == 0 {
-				indexHTML, _ := distFS.(fs.ReadFileFS).ReadFile("index.html")
-				w.Header().Set("Content-Type", "text/html; charset=utf-8")
-				w.WriteHeader(http.StatusOK)
-				_, _ = w.Write(indexHTML)
-				return
-			}
-			fileServer.ServeHTTP(w, r)
+			s.serveSPA(distFS, fileServer, w, r)
 		})
 	}
 }
+
+func (s *Server) serveSPA(
+	distFS fs.FS,
+	fileServer http.Handler,
+	w http.ResponseWriter,
+	r *http.Request,
+) {
+	readFS, ok := distFS.(fs.ReadFileFS)
+	if !ok {
+		http.Error(w, "filesystem error", http.StatusInternalServerError)
+
+		return
+	}
+
+	// Try to serve the file; fall back to index.html for SPA routing.
+	f, err := readFS.ReadFile(r.URL.Path[1:])
+	if err != nil || len(f) == 0 {
+		indexHTML, _ := readFS.ReadFile("index.html")
+
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write(indexHTML)
+
+		return
+	}
+
+	fileServer.ServeHTTP(w, r)
+}