[BUG]: Resume analyzer can be very slow due to N+1 DB queries per missing skill #252

Issue Details

Where: backend/controllers/resumeAnalyzer.controller.js
Problem: For each missing skill, it runs Course.find(...) separately (up to 8 skills). This is up to 8 sequential queries.
Impact: Latency spikes; timeouts under load.
Fix steps
Replace per-skill loop with a single query using $or of regexes for all missing skills (or use $in with normalized tokens where possible).
Post-process returned courses by best matching skill.
Add a hard cap on missingTop (already slice(0,8), keep it).