docs: simplify architecture diagram and reorder README

[benvinegar]

• Simplify architecture tree: collapse verbose file-by-file listings into grouped summaries
• Condense deploy model from a separate subsection into a single sentence
• Move Architecture and Security Stack sections below How It Works so readers get the narrative first
• New section order: Why → Quick Start → Config → Ops → Tests → How It Works → Architecture → Security Stack → Security Details

Net: -31 lines. Same information, easier to scan.

[greptile-apps]

Greptile Summary

This PR reorganizes README.md for improved readability without changing any technical content. The architecture diagram was simplified by collapsing verbose file-by-file listings into grouped summaries, the deploy model description was condensed from a subsection into a single clear sentence, and sections were reordered to present the narrative (Why → Quick Start → Config → Ops → Tests → How It Works) before diving into technical details (Architecture → Security Stack → Security Details).

• Simplified architecture tree reduces visual clutter while maintaining all essential information
• Deploy model condensed into one-liner immediately following the architecture diagram
• Section reordering improves first-time reader experience by presenting practical usage before deep technical details
• Net reduction of 31 lines improves scannability

All technical information is preserved and accurately represented in the new structure.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• Documentation-only change that improves readability by simplifying the architecture diagram and reordering sections for better flow. No code changes, no logic changes, all information preserved
• No files require special attention

Important Files Changed

Filename	Overview
README.md	Documentation reorganization: simplified architecture diagram, condensed deploy model description, reordered sections for better narrative flow

_{Last reviewed commit: c6c4bba}