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/scripts/setup.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -e
+
+# Create venv if not exists (idempotent)
+if [ ! -d ".venv" ]; then
+    uv venv .venv
+fi