Alumni directory with search & filters (real data)

[MrImmortal09]

Context

Replace the seeded featuredAlumni array on /directory with paginated DB results. This is the most-visited page, so performance and UX matter.

Acceptance criteria

• /directory fetches from DB (server component)
• Filters: branch, batch range, city, country, company, role (student / alumnus / faculty)
• Full-text search across name, headline, current company, city
• Pagination — cursor-based, 24 per page
• Respects per-field privacy (Per-field privacy controls on profiles #14) — hidden fields never appear in search indexes
• Empty-state copy when filters yield no results
• Query params reflect filter state (shareable URLs)
• Load time under 500 ms for an empty query on a hot DB

Depends on #8, #12, #14.