refactor(ci): shift quality checks to pre-commit, CI as 2nd pass (#34)

* refactor(ci): shift quality checks to pre-commit, CI as 2nd pass

- Remove ci.yml (lint, security, pytest were only for EPUB scripts)
- Move EPUB build to pre-commit local hook (runs on .md changes)
- Add check_cross_references.py, check_mermaid.py, check_links.py scripts
- Add markdown-lint, cross-references, mermaid-syntax, link-check as
  pre-commit hooks — mirrors all 4 CI doc-check jobs locally
- Remove spell check job from docs-check.yml (breaks on translations)
- Refactor docs-check.yml to reuse scripts/ instead of inline Python
- Add .markdownlint.json config shared by pre-commit and CI
- Update CONTRIBUTING.md with required dependencies and hook table

* fix(ci): resolve all CI check failures in docs-check workflow

- fix(check_cross_references): skip code blocks and inline code spans
  to avoid false positives from documentation examples; fix emoji
  heading anchor generation (rstrip not strip); add blog-posts,
  openspec, prompts, .agents to IGNORE_DIRS; ignore README.backup.md
- fix(check_links): strip trailing Markdown punctuation from captured
  URLs; add wikipedia, api.github.com to SKIP_DOMAINS; add placeholder
  URL patterns to SKIP_URL_PATTERNS; add .agents/.claude to IGNORE_DIRS
- fix(check_mermaid): add --no-sandbox puppeteer config support via
  MERMAID_PUPPETEER_NO_SANDBOX env var for GitHub Actions Linux runners
- fix(docs-check.yml): pass MERMAID_PUPPETEER_NO_SANDBOX=true to mermaid job
- fix(content): repair broken anchors in README.md, 09-advanced-features;
  fix #plugins -> #claude-code-plugins in claude_concepts_guide.md;
  remove non-existent ./docs/performance.md placeholder links; fix
  dependabot alerts URL in SECURITY_REPORTING.md; update auto-mode URL
  in resources.md; use placeholder pattern for 07-plugins example URL
- remove README.backup.md (stale file)

* fix(check-scripts): fix strip_code_blocks regex and URL fragment handling

- fix regex in strip_code_blocks to avoid conflicting MULTILINE+DOTALL
  flags that could fail to strip indented code fences; use DOTALL only
- strip URL fragments (#section) before dispatching link checks to avoid
  false-positive 404s on valid URLs with anchor fragments

* fix(check-scripts): fix anchor stripping, cross-ref enforcement, and mermaid temp file cleanup

- heading_to_anchor: use .strip("-") instead of .rstrip("-") to also strip leading hyphens
  produced by emoji-prefixed headings, preventing false-positive anchor errors
- check_cross_references: always exit with main()'s return code — filesystem checks
  should block pre-commit unconditionally, not silently pass on errors
- check_mermaid: wrap file-processing loop in try/finally so the puppeteer config
  temp file is cleaned up even if an unexpected exception (e.g. UnicodeDecodeError) occurs
- docs-check.yml: remove now-unused CROSS_REF_STRICT env var

* fix(scripts): fix anchor stripping and mermaid output path

- Replace .strip('-') with .rstrip('-') in heading_to_anchor() so leading
  hyphens from emoji-prefixed headings are preserved, matching GitHub's
  anchor generation behaviour.
- Use Path.with_suffix('.svg') in check_mermaid.py instead of
  str.replace('.mmd', '.svg') to avoid replacing all occurrences of .mmd
  in the full temp path.

README.md

@@ -19,7 +19,7 @@
 
 Go from typing `claude` to orchestrating agents, hooks, skills, and MCP servers — with visual tutorials, copy-paste templates, and a guided learning path.
 
-**[Get Started in 15 Minutes](#-get-started-in-15-minutes)** | **[Find Your Level](#-not-sure-where-to-start)** | **[Browse the Feature Catalog](CATALOG.md)**
+**[Get Started in 15 Minutes](#get-started-in-15-minutes)** | **[Find Your Level](#not-sure-where-to-start)** | **[Browse the Feature Catalog](CATALOG.md)**
 
 ---
 
@@ -28,8 +28,8 @@ Go from typing `claude` to orchestrating agents, hooks, skills, and MCP servers
 - [The Problem](#the-problem)
 - [How Claude How To Fixes This](#how-claude-how-to-fixes-this)
 - [How It Works](#how-it-works)
-- [Not Sure Where to Start?](#-not-sure-where-to-start)
-- [Get Started in 15 Minutes](#-get-started-in-15-minutes)
+- [Not Sure Where to Start?](#not-sure-where-to-start)
+- [Get Started in 15 Minutes](#get-started-in-15-minutes)
 - [What Can You Build With This?](#what-can-you-build-with-this)
 - [FAQ](#faq)
 - [Contributing](#contributing)
@@ -92,7 +92,7 @@ The real power is in combining features. Learn to wire slash commands + memory +
 
 Run `/lesson-quiz [topic]` after each module. The quiz pinpoints what you missed so you can fill gaps fast.
 
-**[Get Started in 15 Minutes](#-get-started-in-15-minutes)**
+**[Get Started in 15 Minutes](#get-started-in-15-minutes)**
 
 ---
 
@@ -173,7 +173,7 @@ cp -r 03-skills/code-review ~/.claude/skills/
 # Follow the learning path for guided setup
 ```
 
-**[View the Full Installation Reference](#installation-quick-reference)**
+**[View the Full Installation Reference](#get-started-in-15-minutes)**
 
 ---
 
@@ -222,7 +222,7 @@ You already have Claude Code installed. The only thing between you and 10x produ
 
 MIT licensed. Free forever. Clone it, fork it, make it yours.
 
-**[Start the Learning Path ->](LEARNING-ROADMAP.md)** | **[Browse the Feature Catalog](CATALOG.md)** | **[Get Started in 15 Minutes](#-get-started-in-15-minutes)**
+**[Start the Learning Path ->](LEARNING-ROADMAP.md)** | **[Browse the Feature Catalog](CATALOG.md)** | **[Get Started in 15 Minutes](#get-started-in-15-minutes)**
 
 ---