docs: complete Phase 2 - Core Content Restructure

Restructured main documentation pages with extensibility focus.

Changes:
- Restructured docs/index.md to 93 lines (target: 80-120) ✓
  - Emphasized customization and extensibility in opening paragraphs
  - Removed cost-focused sections
  - Added navigation links to new pages
  - Kept essential three-phase workflow diagram

- Updated docs/features.md to 182 lines
  - Moved Configuration & Customization to #1 position
  - Moved Template System to #2 position
  - Moved Cost Efficiency to bottom (#9 position)
  - Added cross-references to customization.md and workflows.md
  - Renamed "Cost Efficiency" to "Subscription-Based Model"

- Created docs/customization.md (537 lines, allowed to exceed 150)
  - Merged hooks.md and templates.md content
  - Added 3+ real-world customization scenarios:
    1. React + TypeScript project with quality gates
    2. REST API with security requirements
    3. Monorepo multi-package coordination
  - Documented all 7 hooks with examples
  - Documented all 5 templates with customization guidelines
  - Included best practices section

- Created docs/workflows.md (485 lines)
  - 5 distinct workflow patterns with diagrams
  - Detailed plan mode integration guide (priority pattern)
  - Iterative refinement pattern
  - Multi-session projects pattern
  - Parallel development pattern
  - Spike → production pattern

Success Criteria Met:
- Extensibility emphasized in all pages ✓
- Cost de-emphasized (moved to bottom, renamed) ✓
- workflows.md has 5 patterns (target: 3+) ✓
- customization.md has 3+ real-world scenarios ✓
- All cross-references added ✓

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: claude