feat: restructure into a multi-extension plugin framework for Claude Code and agy

Replace the skills-only SSoT (skills/<name>/SKILL.md) with plugins/<name>/,
where a plugin can bundle skills, MCP servers, lifecycle hooks, rules,
commands, and agents. scripts/generate_plugins.py now discovers plugins
from one or more layered --source roots and emits real per-target trees
(dist/claude-code/** + .claude-plugin/marketplace.json, dist/agy/**),
translating hooks.json/mcp.json between Claude Code's and agy's actual
schemas instead of only fanning out flat skill lists.

Adds a private-overlay build path (--source/--private-repo/--out/
--install-local) so a second, non-public repo (PII, tokens, personal-only
plugins) can extend or override the public plugin set without either repo
touching the other's history — private builds default to a gitignored
dist-private/ and never land in tracked output.

Drops install.sh and descriptions.json: both only ever covered skills and
pre-date the native plugin marketplace; both tools now install the plugin
marketplace the documented way (Claude Code's /plugin marketplace add,
agy's plugins.json entries). CI path filters move to plugins/**, and the
workflow gains workflow_dispatch for a manual re-trigger.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014YVWWAnvR5TDQzmfY3RXG9

dist/claude-code/readme-sync-audit/.claude-plugin/plugin.json

@@ -0,0 +1,6 @@
+{
+  "name": "readme-sync-audit",
+  "description": "Analyzes repository delta since the last documentation update and synchronizes the README.md with the current codebase state.",
+  "version": "1.2.0",
+  "author": "Rootiest"
+}

dist/claude-code/readme-sync-audit/skills/readme-sync-audit/SKILL.md

@@ -0,0 +1,41 @@
+---
+name: readme-sync-audit
+description: Analyzes repository delta since the last documentation update and synchronizes the README.md with the current codebase state.
+version: 1.2.0
+user-invocable: true
+author: Rootiest
+---
+
+# README Synchronization & Audit Skill
+
+## **Objective**
+To ensure the `README.md` serves as a "Single Source of Truth" by programmatically aligning documentation with the actual state of the codebase. This skill prioritizes accuracy and the removal of obsolete instructions.
+
+## **Execution Protocol**
+
+### **Phase 1: Delta Analysis**
+1. **Time-Travel Check**: Locate the last commit where `README.md` was modified.
+2. **Feature Diff**: Analyze all code changes (files added, functions modified, dependencies updated) from that commit to the present `HEAD`.
+3. **Extraction**: Identify new environment variables, CLI flags, installation steps, or logic changes that are not yet documented.
+
+### **Phase 2: The Pruning & Update Audit**
+Perform a line-by-line comparison of the existing README against the current code:
+*   **Prune**: Remove any setup steps, dependencies, or "Coming Soon" features that no longer exist or have been replaced.
+*   **Correct**: Update version numbers, file paths, and command-line examples to match the current implementation.
+*   **Synthesize**: Add concise documentation for new features identified in Phase 1.
+
+### **Phase 3: Structural Integrity Check**
+Ensure the updated README includes (or updates) these critical sections:
+1. **Quick Start**: Are the commands (e.g., `cargo run`, `npm start`) still the primary entry points?
+2. **Configuration**: Are all current `.env` or config keys listed?
+3. **Usage Examples**: Do the provided code snippets actually compile/run with the current API?
+
+## **Constraints & Rules**
+*   **Minimalism**: Maintain the existing tone of the README. Do not add "fluff" or marketing language unless the original document uses it.
+*   **No Hallucinations**: If a feature's purpose is unclear from the code diff, add a `TODO` comment or ask the user for clarification rather than guessing.
+*   **Markdown Standards**: Use standard GFM (GitHub Flavored Markdown). Ensure all code blocks have the correct language identifier for syntax highlighting.
+
+## **Trigger Scenarios**
+* **Direct Command:** The user invokes `/readme-sync-audit` or `/update-docs`.
+* **Natural Language:** User says "Update the docs" or "Sync the README with my recent changes."
+* **Contextual Suggestion:** Trigger automatically if the model detects significant changes to public APIs, CLI arguments, or environment variables without a corresponding documentation update.