docs(issue-10): update Stage 2 plan with correct Hugo Templates approach

The previous Stage 2 plan was based on incorrect understanding of the
root cause. It focused on fixing workflow logic, but the real issue is
that we need to use Hugo Templates Framework's built-in incremental
capabilities instead of custom logic.

Updated Plan Overview:
- Replace custom workflow logic with federated-build.sh
- Use --preserve-base-site flag for incremental documentation updates
- Create federation-modules.json configuration
- Remove custom 'Atomic Merge' sections entirely

Root Cause Analysis:
- Problem: Custom workflow logic cannot handle content preservation
- Solution: Hugo Templates Framework has preserve-base-site strategy
- Benefit: Automatic downloading and merging of existing GitHub Pages content

Technical Approach:
- Step 2.1: Create federation-modules.json configuration
- Step 2.2: Replace workflow sections with federated-build.sh calls
- Step 2.3: Configure preserve-base-site for incremental updates
- Step 2.4: Local testing and validation
- Step 2.5: Commit all changes

This approach leverages the production-ready federated build system
(140 tests, 100% pass rate) instead of trying to fix custom logic.

Related: #10, Epic: #2
Updates: Stage 2 plan based on Hugo Templates Framework analysis
Previous: Custom workflow fix approach (incorrect)

Author: InfoTech.io Bot