feat(core): add review moderation, project watchlist, advanced search, and Soroban event indexer (#447, #448, #451, #449)

[orunganiekan]

Summary

• Add review spam detection with client heuristics, velocity/CAPTCHA checks, admin moderation queue (risk score, bulk actions, ban, stats), and API routes.
• Add wallet-scoped project watchlist (max 20), navbar badge, profile view with category filter/trending/notifications, and discover/detail watchlist controls.
• Add advanced search filters (URL-encoded), presets, saved searches (max 10), autocomplete, and CSV export.
• Add Soroban event indexer service plus /api/events with circuit breaker and historical replay support.

Closes #447
Closes #448
Closes #451
Closes #449

Test plan

• Submit reviews with short/ALL CAPS content and verify spam warnings and moderation flagging
• Add/remove projects from watchlist on discover and project detail; verify navbar count and profile watchlist
• Apply advanced filters and presets on Discover; save/run searches from profile; export CSV
• GET /api/events returns indexed demo/replayed events
• Admin Spam Queue shows flagged reviews with risk scores and supports bulk approve/reject/ban

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