feat(sproutclaw): modularize webui, extensions, and agent config layout

Restructure local extensions into per-feature directories, split WebUI
into backend modules with slash commands and systemd support, and track
prompts/skills under .pi/agent for portable Gitea deployment.

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/coding-agent/npm-shrinkwrap.json

@@ -1321,7 +1321,8 @@
 			"license": "MIT",
 			"bin": {
 				"jiti": "lib/jiti-cli.mjs"
-			}
+			},
+			"peer": true
 		},
 		"node_modules/json-bigint": {
 			"version": "1.0.0",
@@ -1774,7 +1775,8 @@
 			"license": "MIT",
 			"funding": {
 				"url": "https://github.com/sponsors/colinhacks"
-			}
+			},
+			"peer": true
 		},
 		"node_modules/zod-to-json-schema": {
 			"version": "3.25.2",