feat: open-source release prep, audit fixes, and deploy hardening

Production deploy completed (DigitalOcean Droplet, self-hosted Supabase,
Caddy + Let's Encrypt, GitHub Actions auto-deploy on push to main, daily
pg_dumpall backups). This commit lands the work that came out of the
deep audit pass and the open-source release prep.

Audit fixes:
- Webhook signing secret is now displayed in the settings UI with
  show/hide and copy-to-clipboard; the broken external docs.hackerspace.sh
  link is replaced with a link to the new local docs.
- Settings updateSpaceSettings parameter type now includes
  mission_statement so the field persists.
- members page enforces member_directory_visibility for non-admin viewers
  (admin_only, board_visible, members_visible).
- Mobile responsiveness pass: Projects Kanban grid, Members + Payments
  tables (column hiding on small screens), Proposal tally + voting
  buttons (2-col on mobile).

Open-source release scaffolding:
- LICENSE (MIT).
- CONTRIBUTING.md with dev setup, conventions, PR flow.
- SECURITY.md with disclosure policy.
- CHANGELOG.md.
- docs/WEBHOOKS.md with Node and Python signature verification examples.
- README.md rewritten for an open-source audience.

Removed v0/Vercel references:
- @vercel/analytics dependency removed.
- app/layout.tsx no longer imports Analytics, drops generator: 'v0.app'.
- Canonical deployment docs (docs/DEPLOYMENT.md, docs/README.md,
  docs/ARCHITECTURE.md, DATABASE.md, CLAUDE.md, README.md) now describe
  the self-hosted Droplet target only.
- e2e console-error check no longer filters [v0] noise.

Landing page:
- GitHub icon link to the public repo in the nav and footer.

docs/README.md

@@ -74,7 +74,7 @@ A comprehensive member management platform for hackerspaces, makerspaces, and co
 | Database | Supabase PostgreSQL |
 | Auth | Supabase Auth |
 | Real-time | Supabase Realtime |
-| Hosting | Vercel |
+| Hosting | Self-hosted DigitalOcean Droplet (Docker, Caddy) |
 
 ---
 
@@ -174,11 +174,9 @@ All database access is protected by RLS policies:
 
 ## Deployment
 
-### Vercel
+### DigitalOcean Droplet (production)
 
-1. Connect GitHub repository
-2. Set environment variables in Vercel dashboard
-3. Deploy automatically on push to main
+See [DEPLOYMENT.md](./DEPLOYMENT.md) for the at-a-glance flow and [DEPLOY_DO_SELFHOSTED.md](./DEPLOY_DO_SELFHOSTED.md) for the end-to-end provisioning procedure. Every push to `main` triggers GitHub Actions, which runs the deploy script on the Droplet over SSH.
 
 ### Database Migrations
 
@@ -205,10 +203,10 @@ Migrations must be run manually via Supabase SQL Editor:
 
 Add console logs in server actions:
 ```typescript
-console.log('[v0] User:', user?.id, 'Space:', member?.space_id)
+console.log('[app] User:', user?.id, 'Space:', member?.space_id)
 ```
 
-View logs in Vercel Function logs or terminal.
+View logs with `journalctl -u hackerspace-app -f` on the Droplet, or in the dev server terminal locally.
 
 ---