Docs/dbms indexing query recovery

[codewithzubair07]

Closes #10

Changes

• ch6: Indexing and Hashing (dense/sparse index, B+ Tree, static/dynamic hashing)
• ch7: Query Processing and Optimization (pipeline, join algorithms, heuristics)
• ch8: Recovery and Security (log-based recovery, WAL, checkpoints, shadow paging, SQL injection)

Notes

• Completes all 9 DBMS chapters (ch0–ch8)
• Follows existing subject structure
• Beginner-friendly with examples and exam tips

[vercel]

@jannatfirdous07 is attempting to deploy a commit to the PushkarScripts Team on Vercel.

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[pushkarscripts]

Update app\components\subjects.tsx file as well for it to be complete.

// Update this line
const available = ["ep", "c", "em1", "em2", "oops", "dsc", "os", "ml", "dops"];