App-templates: LLM auto-selects project template based on user requirement

- Add webapp template (FastAPI + SQLite) with INSTRUCTIONS.md and setup.sh
- select_template() scans templates, asks LLM to match; apply_template() copies to workspace
- ensure_workspace() runs setup.sh if present, otherwise falls back to default venv
- INSTRUCTIONS.md injected into planning and execution prompts
- Fix pre-existing clippy warning in kb.rs (filter_map → map)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app-templates/webapp/template.json

@@ -0,0 +1,5 @@
+{
+  "name": "Web 应用",
+  "description": "FastAPI + SQLite 的 Web 应用",
+  "match_hint": "需要前后端、Web 界面、HTTP API、数据库的应用类项目"
+}