Deep review Oracle skills docs and examples

[krisrice]

Summary

This PR continues the deep accuracy pass across the Oracle DB skills repo, focusing on monitoring, performance, security, and admin guides.

What changed

• corrected invalid historical tablespace/AWR example queries in space-management.md
• corrected Autonomous Database automatic indexing mode guidance in index-strategy.md
• tightened PGA_AGGREGATE_LIMIT guidance in memory-tuning.md
• fixed RMAN point-in-time recovery examples to use SET UNTIL consistently
• corrected Data Guard failover guidance around FAILOVER ... IMMEDIATE
• repaired the broken AIM example in inmemory-column-store.md
• fixed privilege/VPD/undo examples in the highest-priority security/admin files
• removed remaining whitespace blockers in reviewed docs

Validation

• targeted line-by-line review of the highest-risk files
• Oracle doc cross-checks for version-sensitive syntax and view/package usage
• git diff --check clean for reviewed skill areas

Notes

This is a documentation and syntax accuracy pass, not runtime validation against a live Oracle instance.