fix: trim DOCKERHUB.md to stay under Docker Hub's 25KB limit

[aliasunder]

Summary

• Docker Hub truncates README content at 25,000 bytes — the current DOCKERHUB.md is 25,288 bytes, cutting off the Deployment Options table mid-row (AWS/SST guide link is unreadable)
• Excludes four verbose prose sections (How It Works, Hybrid Search, Memory, Tasks) from the generated output — these are already covered by the feature bullet list, which links to each section on GitHub
• Output drops from 25,288 → 19,983 bytes (~5KB of headroom for future growth)

Test plan

• npm run generate:dockerhub-readme reports 19,983 bytes (under 25,000 limit, under 24,000 warning threshold)
• Template drift tests pass (npm test -- --run templates)
• Build passes
• After merge + next release: verify Deployment Options table renders fully on Docker Hub

🤖 Generated with Claude Code

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[umm-actually]

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