feat: add go-patterns skill

.skills/go-patterns/SKILL.md

@@ -0,0 +1,42 @@
+---
+name: go-patterns
+description: Go project patterns — endpoint checklist, error handling, HTMX responses, dependency policy. Use when writing Go code, adding endpoints, or reviewing Go PRs.
+---
+
+# Go project patterns
+
+## New endpoint checklist
+1. Define request/response types in `types.go`
+2. Write handler in `handlers.go` using `http.HandlerFunc`
+3. Add route in `routes.go`
+4. Write table-driven test in `handlers_test.go`
+5. Run `task check` before committing
+
+## Error handling pattern
+```go
+if err != nil {
+    return fmt.Errorf("descriptiveOperation: %w", err)
+}
+```
+Never log and return — do one or the other.
+
+## HTMX response pattern
+```go
+func (h *Handler) ListItems(w http.ResponseWriter, r *http.Request) {
+    items, err := h.store.List(r.Context())
+    if err != nil {
+        http.Error(w, "failed to list items", http.StatusInternalServerError)
+        return
+    }
+    if r.Header.Get("HX-Request") == "true" {
+        h.templates.Render(w, "items/_list", items)
+        return
+    }
+    h.templates.Render(w, "items/index", items)
+}
+```
+
+## Dependency policy
+- Prefer stdlib: `net/http`, `encoding/json`, `database/sql`
+- Allowed without justification: `testify`, `slog`, `templ`, `sqlc`
+- Needs justification in commit message: anything else