refactor: extract skills from commands across 8 plugins

Refactored commands to extract reusable skills following the
Commands → Skills separation pattern. Each command is now <50 lines
and references skill files for detailed knowledge.

Plugins refactored:
- claude-config-maintainer: 5 commands → 7 skills
- code-sentinel: 3 commands → 2 skills
- contract-validator: 5 commands → 6 skills
- data-platform: 10 commands → 6 skills
- doc-guardian: 5 commands → 6 skills (replaced nested dir)
- git-flow: 8 commands → 7 skills

Skills contain: workflows, validation rules, conventions,
reference data, tool documentation

Commands now contain: YAML frontmatter, agent assignment,
skills list, brief workflow steps, parameters

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/claude-config-maintainer/skills/lint-rules.md

@@ -0,0 +1,136 @@
+# CLAUDE.md Lint Rules
+
+This skill defines all linting rules for validating CLAUDE.md files.
+
+## Rule Categories
+
+### Security Rules (SEC)
+
+| Rule | Description | Severity | Auto-fix |
+|------|-------------|----------|----------|
+| SEC001 | Hardcoded absolute paths | Warning | Yes |
+| SEC002 | Potential secrets/API keys | Error | No |
+| SEC003 | Hardcoded IP addresses | Warning | No |
+| SEC004 | Exposed credentials patterns | Error | No |
+| SEC005 | Hardcoded URLs with tokens | Error | No |
+| SEC006 | Environment variable values (not names) | Warning | No |
+
+### Structure Rules (STR)
+
+| Rule | Description | Severity | Auto-fix |
+|------|-------------|----------|----------|
+| STR001 | Missing required sections | Error | Yes |
+| STR002 | Invalid header hierarchy (h3 before h2) | Warning | Yes |
+| STR003 | Orphaned content before first header | Info | No |
+| STR004 | Excessive nesting depth (>4 levels) | Warning | No |
+| STR005 | Empty sections | Warning | Yes |
+| STR006 | Missing section content | Warning | No |
+
+### Content Rules (CNT)
+
+| Rule | Description | Severity | Auto-fix |
+|------|-------------|----------|----------|
+| CNT001 | Contradictory instructions | Error | No |
+| CNT002 | Vague or ambiguous rules | Warning | No |
+| CNT003 | Overly long sections (>100 lines) | Info | No |
+| CNT004 | Duplicate content | Warning | No |
+| CNT005 | TODO/FIXME in production config | Warning | No |
+| CNT006 | Outdated version references | Info | No |
+| CNT007 | Broken internal links | Warning | No |
+
+### Format Rules (FMT)
+
+| Rule | Description | Severity | Auto-fix |
+|------|-------------|----------|----------|
+| FMT001 | Inconsistent header styles | Info | Yes |
+| FMT002 | Inconsistent list markers | Info | Yes |
+| FMT003 | Missing code block language | Info | Yes |
+| FMT004 | Trailing whitespace | Info | Yes |
+| FMT005 | Missing blank lines around headers | Info | Yes |
+| FMT006 | Inconsistent indentation | Info | Yes |
+
+### Best Practice Rules (BPR)
+
+| Rule | Description | Severity | Auto-fix |
+|------|-------------|----------|----------|
+| BPR001 | No Quick Start section | Warning | No |
+| BPR002 | No Critical Rules section | Warning | No |
+| BPR003 | Instructions without examples | Info | No |
+| BPR004 | Commands without explanation | Info | No |
+| BPR005 | Rules without rationale | Info | No |
+| BPR006 | Missing plugin integration docs | Info | No |
+
+## Anti-Pattern Examples
+
+### SEC002: Hardcoded Secrets
+```markdown
+# BAD
+API_KEY=sk-1234567890abcdef
+
+# GOOD
+API_KEY=$OPENAI_API_KEY  # Set via environment
+```
+
+### SEC001: Hardcoded Paths
+```markdown
+# BAD
+Config file: /home/john/projects/myapp/config.yml
+
+# GOOD
+Config file: ./config.yml
+Config file: $PROJECT_ROOT/config.yml
+```
+
+### CNT001: Contradictory Rules
+```markdown
+# BAD
+- Always use TypeScript
+- JavaScript files are acceptable for scripts
+
+# GOOD
+- Always use TypeScript for source code
+- JavaScript (.js) is acceptable only for config files and scripts
+```
+
+### CNT002: Vague Instructions
+```markdown
+# BAD
+- Be careful with the database
+
+# GOOD
+- Never run DELETE without WHERE clause
+- Always backup before migrations
+```
+
+### STR002: Invalid Hierarchy
+```markdown
+# BAD
+# Main Title
+### Skipped Level
+
+# GOOD
+# Main Title
+## Section
+### Subsection
+```
+
+## Output Format
+
+```
+[SEVERITY] RULE_ID: Description (line N)
+  | Context line showing issue
+  |          ^^^^^^ indicator
+  +-- Explanation of problem
+
+  Suggested fix:
+  - old line
+  + new line
+```
+
+## Severity Levels
+
+| Level | Meaning | Action |
+|-------|---------|--------|
+| Error | Must fix | Blocks commit |
+| Warning | Should fix | Review recommended |
+| Info | Consider fixing | Optional improvement |