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.

.claude-plugin/plugin.json

@@ -0,0 +1,11 @@
+{
+  "name": "agent-loop",
+  "version": "0.1.0",
+  "description": "Autonomous generator-evaluator agent loop for long-running coding tasks. Plan with /agent-loop:init, then execute with /agent-loop:run.",
+  "author": {
+    "name": "Sheldon"
+  },
+  "repository": "https://git.jagfly.com/sheldon/loop-loop.git",
+  "license": "MIT",
+  "keywords": ["agent", "loop", "autonomous", "generator", "evaluator", "harness"]
+}