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/contract-validator/skills/dependency-analysis.md

@@ -0,0 +1,57 @@
+# Skill: Dependency Analysis
+
+Analyze dependencies between plugins including shared MCP servers and data flows.
+
+## Dependency Types
+
+| Type | Line Style | Meaning |
+|------|------------|---------|
+| Required | Solid (`-->`) | Plugin cannot function without this |
+| Optional | Dashed (`-.->`) | Plugin works with reduced functionality |
+| Internal | Dotted (`...>`) | Self-dependency within same plugin |
+| Shared MCP | Double (`==>`) | Plugins share same MCP server instance |
+
+## Shared MCP Server Detection
+
+Check each plugin's `.mcp.json` for server definitions. Plugins with identical MCP server names share that server.
+
+**Common shared servers:**
+- `gitea` - Used by projman, pr-review
+- `netbox` - Used by cmdb-assistant
+- `data-platform` - Used by data-platform
+- `viz-platform` - Used by viz-platform
+
+## Data Flow Patterns
+
+### Data Producers
+- `read_csv`, `read_parquet`, `read_json` - File loaders
+- `pg_query`, `pg_execute` - Database queries
+- `filter`, `select`, `groupby`, `join` - Transformations
+
+### Data Consumers
+- `describe`, `head`, `tail` - Data inspection
+- `to_csv`, `to_parquet` - File writers
+- `chart_create` - Visualization
+
+### Cross-Plugin Flows
+| Producer | Consumer | Data Type |
+|----------|----------|-----------|
+| data-platform | viz-platform | `data_ref` |
+| projman | pr-review | issues/lessons |
+| gitea wiki | projman | lessons learned |
+
+## Required vs Optional
+
+- **Required**: Consumer has no default/fallback (ERROR if missing)
+- **Optional**: Consumer works without producer (WARNING if missing)
+
+Determined by:
+- Issue severity from `validate_data_flow`
+- Tool docs stating "requires" vs "uses if available"
+
+## MCP Tools
+
+| Tool | Purpose |
+|------|---------|
+| `validate_data_flow` | Verify producer/consumer relationships |
+| `generate_compatibility_report` | Get full dependency data |