feat: agent loop harness with Claude Code plugin support

Generator-evaluator architecture with iterative context-reset for
long-running coding tasks. Ships as a Claude Code plugin — install
with /plugin and use /agent-loop:init, /agent-loop:plan, /agent-loop:run.

init.sh.example

@@ -0,0 +1,56 @@
+#!/bin/bash
+# Project-specific initialization for the agent loop.
+# Copy this to .loop/init.sh and customize for your project.
+#
+# This script runs at the start of each loop.sh invocation to ensure
+# the development environment is ready. Keep it idempotent (safe to run multiple times).
+
+set -euo pipefail
+
+echo "[init] Setting up development environment..."
+
+# --- Dependencies ---
+# Uncomment and adapt for your project:
+
+# Node.js
+# if [ -f package.json ]; then
+#     npm install --silent
+# fi
+
+# Python
+# if [ -f requirements.txt ]; then
+#     pip install -q -r requirements.txt
+# fi
+
+# Go
+# if [ -f go.mod ]; then
+#     go mod download
+# fi
+
+# Rust
+# if [ -f Cargo.toml ]; then
+#     cargo build --quiet
+# fi
+
+# --- Dev Server ---
+# Start if not already running:
+
+# if ! lsof -i :3000 &>/dev/null; then
+#     npm run dev &
+#     sleep 3
+# fi
+
+# --- Database ---
+# Run migrations if needed:
+
+# npm run migrate
+# python manage.py migrate
+# alembic upgrade head
+
+# --- Verify ---
+# Quick smoke test:
+
+# npm run typecheck
+# npm run test -- --run --silent
+
+echo "[init] Environment ready."