fix: ADO rendering fixes, dismissal status, and docs overhaul

[dsiddharth2]

Summary

• Dismissal thread status: PostFixReplyActivity now honors the status parameter — dismissed findings resolve as WONT_FIX instead of incorrectly using FIXED
• ADO work item auto-linking: All PR ID references (#6718) wrapped in backticks to prevent ADO from rendering them as linked PBIs/Bugs
• Code suggestion rendering: Added newline before code fences in suggestions so ADO renders proper code blocks instead of inline backtick text
• README slimmed: 472 → 131 lines — moved detailed content to docs/, kept essentials
• Architecture docs rewritten: Reflects actual current codebase (batch orchestration, two-pass review, risk classifier, dismissals, smart diff, sliding window)
• Feature docs updated: Dismissal handling in fix-verification.md, ADO rendering notes in post-findings.md

Test plan

• All 68 unit tests pass
• Verify ADO PR summary no longer auto-links PR IDs to work items
• Verify code suggestion blocks render as formatted code in ADO comments
• Verify dismissed findings resolve threads with WONT_FIX status