feat: add agent scaffold (context-sync, skills, context tasks) (#2)

.context/skills/go-patterns.md

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+# Skill: 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

.context/skills/htmx-patterns.md

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+# Skill: HTMX patterns
+
+## Default attributes
+Always include on interactive elements:
+- `hx-indicator` for loading states
+- `hx-swap="innerHTML"` as default (explicit over implicit)
+- `hx-target` pointing to a specific ID, never `this` in production
+
+## Form pattern
+```html
+<form hx-post="/items" hx-target="#item-list" hx-swap="beforeend" hx-indicator="#spinner">
+  <input type="text" name="title" required>
+  <button type="submit">Add</button>
+  <span id="spinner" class="htmx-indicator">...</span>
+</form>
+```
+
+## Server-sent validation errors
+Return 422 with the error fragment, swap into the form's error container:
+```html
+hx-target-422="#form-errors"
+```
+
+## Prefer hypermedia over JSON
+If the endpoint returns data for display, return an HTML fragment.
+Only use JSON for machine-to-machine APIs or when a non-browser client needs it.