docs: Refactor architecture into dedicated file

[chadmf]

Summary

Extract detailed architecture content from README.md into a comprehensive dedicated
architecture document, making the README more concise and scannable.

Changes

New File: docs/architecture.md (650+ lines)

Complete architecture documentation covering:

Component Details:

• Global Load Balancer configuration and failover
• AAP deployment (DC1 active, DC2 passive)
• AAP database replication (logical replication)
• EDB PostgreSQL cluster replication (streaming + WAL)

Network Connectivity:

• User → GLB → AAP data flow
• AAP → PostgreSQL connections
• Inter-datacenter replication topology
• Network requirements and bandwidth recommendations

Data Flow:

• Write operations (6-step flow diagram)
• Read operations (query routing strategy)
• Backup flow (8-step process)
• Failover service behavior

Additional Topics:

• Scaling strategies (horizontal, vertical, geographic)
• DR scenarios overview
• AAP cluster management and EFM integration
• Related architecture documentation links

Updated: README.md

Reduced from 221 lines to 167 lines (-25%)

Improvements:

• ✅ More concise and scannable
• ✅ Added "Quick Links" section
• ✅ Better organization (Overview, Installation, Architecture, Operations)
• ✅ Removed license/copyright section
• ✅ Clear link to detailed architecture.md
• ✅ Focused on getting started

Retained:

• Title and quick start prominence
• Documentation index links
• Overview with key features
• Installation guides table
• Brief architecture overview with diagram
• Operations links
• Repository structure
• Contributing guidelines

Updated: docs/INDEX.md

Architecture section enhanced:

• Added architecture.md as primary comprehensive reference
• Created comparison table with read times
• Listed topics covered in architecture.md
• Maintained links to platform-specific docs

Benefits

For New Users

• Faster onboarding: README is concise and focused
• Progressive disclosure: Brief overview → detailed docs
• Clear navigation: Easy to find what you need

For Technical Users

• Comprehensive reference: All architecture in one place
• Easy linking: Reference specific architecture topics
• Better organization: Clear table of contents

For Maintainers

• Better separation: README for overview, architecture.md for details
• Easier updates: Architecture changes isolated to one file
• Cleaner README: More professional first impression

File Changes

docs/architecture.md         +650 lines (new file)
README.md                    -54 lines (simplified)
docs/INDEX.md                +15 lines (enhanced)

Standards Compliance

• ✅ TOC for navigation (architecture.md > 200 lines)
• ✅ Lowercase filename with hyphens
• ✅ Relative paths only
• ✅ Code blocks with language tags
• ✅ Consistent terminology
• ✅ All cross-references validated

Testing

• ✅ All internal links verified
• ✅ Cross-references between docs work
• ✅ README flows well and is easy to scan
• ✅ Architecture.md comprehensive and well-organized

Checklist

• Architecture content extracted from README
• Comprehensive architecture.md created
• README simplified and improved
• License/copyright section removed
• docs/INDEX.md updated
• All cross-references validated
• Standards compliant
• Commit message follows guidelines

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Ready to merge - Significantly improves documentation organization and README readability.