Add connection profiles and real-time chat

[jdasilvax]

What changed

• adds connection request confirmation and hides Connect for existing/pending connections
• shows accepted connections on the owner's public profile above Top Supporters
• supports shared Mapathon context, show-more expansion, remove, block, and chat actions
• adds text-only Socket.IO chat UI with history, read tracking, unread counts, connection revocation handling, and login-time unread popup
• adds yellow unread/request indicators in navigation and connection cards
• removes profile coordinates and username fields from account screens
• preserves the latest next-application anonymous/display-name and public-profile-link behavior during conflict resolution

Why

Connections previously had no complete public-profile surface or real-time conversation flow. This adds a scoped connection experience while keeping identity privacy behavior intact.

Validation

• synced and rebased against latest origin/next-application (f1af9049)
• npm ci
• npm run build — passed; 30/30 static pages generated
• git diff --check — passed

Dependency / rollout

Requires the companion API PR that adds the Socket.IO server, message persistence, unread endpoint, authorization, revocation, rate limiting, and tests.

Risks

• Socket.IO must be supported by the production proxy/load balancer and allowed web origins must be configured correctly.
• Existing dependency audit findings remain; this PR intentionally does not broaden scope into dependency upgrades.