Add four agent security and robustness papers

[estelledc]

Summary

• Summarize the remaining gap after the general assistant/browser/mobile round: agent safety and robustness are still underrepresented.
• Add four study-v2 paper notes for AgentDojo, InjecAgent, Privacy Practices of Browser Agents, and Active Environmental Injection.
• Add matching study-review-receipt-v1 receipts, refresh atlas/note-index, and update public scale copy to 1079 papers / 961 projects / 2040 notes.

Evidence Boundary

• All four notes stay STATIC_ANALYSIS / UNVERIFIED.
• No attack benchmark, browser-agent audit, or multimodal robustness suite was executed.

Verification

• node scripts/quality-gate.mjs for all 4 new notes
• npm run audit:content-contract
• npm run atlas
• npm run audit:counts
• npm run audit:links
• npm run audit:wikilinks
• git ls-files -co --exclude-standard -z | node scripts/audit-public-redlines.mjs --stdin0
• npm run build:strict -- --log /tmp/study-20260715-agent-security-round-build-clean.log
• STUDY_CHANGED_FROM=origin/main npm run verify:ci