docs: migrate module documentation to single source of truth

Move 39 documentation files from top-level docs/ into each module's
docs/ folder, accessible via symlinks from docs/modules/. Create
data-model.md files for 10 modules with full schema documentation.
Replace originals with redirect stubs. Remove empty guide stubs.

Modules migrated: tenancy, billing, loyalty, marketplace, orders,
messaging, cms, catalog, inventory, hosting, prospecting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/dev_tools/docs/index.md

@@ -0,0 +1,42 @@
+# Developer Tools
+
+Internal development tools including code quality scanning, test execution, component library, and icon browser.
+
+## Overview
+
+| Aspect | Detail |
+|--------|--------|
+| Code | `dev-tools` |
+| Classification | Internal |
+| Dependencies | None |
+| Status | Active |
+
+## Features
+
+- `component_library` — UI component browser and documentation
+- `icon_browser` — Icon set browser
+- `code_quality` — Code quality scanning and reporting
+- `architecture_validation` — Module architecture validation
+- `security_validation` — Security rule checking
+- `performance_validation` — Performance rule checking
+- `test_runner` — Test execution interface
+- `violation_management` — Architecture violation tracking
+
+## Permissions
+
+No permissions defined (internal module, admin-only access).
+
+## Data Model
+
+- **ArchitectureScan** — Code quality scan results
+- **TestRun** — Test execution records
+
+## API Endpoints
+
+| Method | Path | Description |
+|--------|------|-------------|
+| `*` | `/api/v1/admin/dev-tools/*` | Dev tools API |
+
+## Configuration
+
+No module-specific configuration.