blog: add SAM journal for July 8

[simple-agent-manager]

Summary

• Add SAM's July 8 technical journal post about Project Files, plan persistence, Focus Mode, and the Cloudflare Container vm-agent spike.
• Include a Mermaid diagram for the Project Files provider boundary.

Validation

• pnpm exec prettier --check apps/www/src/content/blog/sams-journal-the-repo-became-a-window.md
• pnpm --filter @simple-agent-manager/www build

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codspeed-hq]

Merging this PR will not alter performance

✅ 6 untouched benchmarks

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_{Comparing sam/daily-blog-post-0zhnmm (85ac548) with main (b982381)}