feat(plugin): ship as Claude Code plugin with 150-line cap and sync command

Turns ClaudeForge into an installable Claude Code plugin and adds the
missing pieces for a clean lifecycle: hard line-cap enforcement, modular
chaining via @path imports, a sync/cleanup command, and Explore-agent
delegation for project discovery.

- .claude-plugin/plugin.json: plugin manifest registering both skills,
  both commands, and the guardian agent (installable via /plugin marketplace
  add alirezarezvani/ClaudeForge && /plugin install claudeforge)
- skill/validator.py: MAX_RECOMMENDED_LINES 300 -> 150 (warning at 120)
- skill/template_selector.py: target_lines capped at 150 across all
  team sizes (solo 75 / small 100 / medium 125 / large 150) so any
  single CLAUDE.md fits within the cap; bigger projects spread content
  across modular sub-files
- skill/analyzer.py: length thresholds, quality scoring, and recommendations
  rebased on the 150 cap (was 300/400)
- skill/generator.py: modular root now emits @path imports next to the
  human-readable links; every sub-CLAUDE.md gets a back-link header
  pointing to ../CLAUDE.md (markdown + @import) for bidirectional chaining
- command/sync-claude-md.md: new /sync-claude-md command that inventories
  every CLAUDE.md, prunes stale references, enforces the 150 cap by
  splitting into sub-files, and repairs the root <-> sub chain
- command/enhance-claude-md.md: discovery phase now delegates the deep
  codebase scan to the Explore subagent to keep context lean
- install.sh / install.ps1: each command in command/ installs as its own
  ~/.claude/commands/<name>.md (legacy bundle backed up on upgrade)
- skill/SKILL.md, CLAUDE.md, README.md, CHANGELOG.md: docs updated for
  the plugin install path, sync command, and new line cap

Verified via smoke test: validator constants, template targets, generator
output line counts across 5 presets (all <= 150), context files with
backlinks, @-import chain in modular root, idempotent merge_with_existing,
validator status transitions at the new cap, analyzer quality differential,
and plugin manifest JSON shape with all referenced paths existing on disk.

README.md

@@ -44,12 +44,15 @@ ClaudeForge is a comprehensive toolkit that eliminates the tedious process of ma
 Core capability for CLAUDE.md analysis, generation, validation, and enhancement
 
 ### 2. **Slash Command** (`/enhance-claude-md`)
-Interactive interface with multi-phase discovery workflow
+Interactive interface with multi-phase discovery workflow. Delegates deep codebase scans to the Explore subagent so the discovery does not bloat the calling session.
 
-### 3. **Guardian Agent** (`claude-md-guardian`)
+### 3. **Slash Command** (`/sync-claude-md`)
+Walks every CLAUDE.md in the project, prunes stale references (removed dependencies, deleted files, dead modular links), enforces the **150-line hard cap per file**, and repairs the root ↔ subdirectory chain (markdown links + `@path` imports). Run after refactors, dependency changes, or before cutting a release.
+
+### 4. **Guardian Agent** (`claude-md-guardian`)
 Background agent for automatic CLAUDE.md maintenance and synchronization
 
-### 4. **Karpathy Guidelines Skill** (`karpathy-guidelines`)
+### 5. **Karpathy Guidelines Skill** (`karpathy-guidelines`)
 Behavioral guardrails — Think Before Coding, Simplicity First, Surgical Changes, Goal-Driven Execution — installed as a standalone skill and automatically embedded into every CLAUDE.md generated or enhanced by `/enhance-claude-md`. Adapted with attribution from the MIT-licensed [forrestchang/andrej-karpathy-skills](https://github.com/forrestchang/andrej-karpathy-skills) repository, inspired by Andrej Karpathy's observations on common LLM coding failure modes.
 
 ---
@@ -58,6 +61,17 @@ Behavioral guardrails — Think Before Coding, Simplicity First, Surgical Change
 
 ### Installation
 
+#### **Claude Code Plugin (recommended)**
+
+ClaudeForge ships as a Claude Code plugin. From any Claude Code session:
+
+```text
+/plugin marketplace add alirezarezvani/ClaudeForge
+/plugin install claudeforge
+```
+
+This installs every component (skills, slash commands, guardian agent) and registers `/enhance-claude-md` and `/sync-claude-md` for any project. Works the same at the user level (available everywhere) or scoped to a single project.
+
 #### **macOS / Linux**
 ```bash
 curl -fsSL https://raw.githubusercontent.com/alirezarezvani/ClaudeForge/main/install.sh | bash