chore: register @ninja/smartblock scope and ignore pnpm-workspace.yaml

- plugin.mod: scope normalized to @ninja and category set to the valid
  "developer" taxonomy entry (via ninja plugin init against the dev registry).
- .gitignore: ignore web/pnpm-workspace.yaml (pnpm-generated allowBuilds file).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -1,3 +1,4 @@
 *.bnp
 *.wasm
 /web/node_modules/
+/web/pnpm-workspace.yaml

plugin.mod

@@ -1,9 +1,9 @@
 [plugin]
 name = "smartblock"
 display_name = "Smart Block"
-scope = "ninja"
+scope = "@ninja"
 version = "1.0.0"
 description = "AI-powered block that generates custom content structures from natural-language prompts and renders them by substituting {{field}} placeholders."
 kind = "plugin"
-categories = ["content"]
+categories = ["developer"]
 tags = ["ai", "content", "blocks", "generative"]