feat(tier2): event branding + UX polish — Block D

Backend
- Migration 0010 adds event_branding (one row per event; all fields
  nullable so a brand-new event renders with defaults)
- BrandingRepo with COALESCE/NULLIF upsert semantics: nil pointer
  preserves the existing value, "" clears the field to NULL
- internal/uploads package: ImageStore interface + LocalFSStore (dev),
  pure-stdlib decode + re-encode that strips EXIF and rejects anything
  that isn't valid JPEG/PNG. Size cap 2 MB, random 16-byte filenames
- GET /events/{id}/branding (viewer+) returns the row plus the
  AllowedFonts list so the frontend picker stays in sync
- PUT /events/{id}/branding (editor+) validates hex colours, font
  allowlist, and refuses image URLs whose path doesn't start with
  /uploads/ (blocks arbitrary-origin <img> smuggling on guest pages)
- POST /uploads/image (authed) → fresh CDN URL; GET /uploads/{file}
  serves with year-long cache (immutable random names)
- GET /access/{token} now embeds the host's branding so the RSVP page
  can render in their colours/font with their logo + cover
- docker-compose mounts a named volume for uploads
- Custom-domain sub-block deferred to Tier 3 per the plan

Frontend
- BrandingCard.vue: colour pickers, font dropdown, logo + cover upload
  with progressive disclosure, live preview pane that re-renders on
  every keystroke
- RSVP page applies branding via CSS vars at the section root, so
  primary colour theme + font cascade through every child card. Cover
  image renders as a banner above the form; logo lands in the header
- Submit button background switches to var(--brand-primary) when set
- Mounted on the event detail page below the guests block

Plus the small UX fixes from the e2e walkthrough:
- Nav: dropped the top-level "Events" link; the logo doubles as the
  home affordance (→ /dashboard when signed in, → / otherwise). Account
  + Billing + Sign out live under a profile dropdown (avatar with
  initials, opens on click, closes on outside-click / Esc / route nav)
- Renamed "Back to dashboard" → "Back to events" across event detail,
  billing, account, and new-event pages

Tests
- TestBrandingGetReturnsDefaults / TestBrandingPutPersists /
  TestBrandingPutRejectsBadInputs / TestUploadAndServeImage /
  TestUploadRejectsNonImage — all pass
- Domain tests for IsValidHexColor + IsAllowedFont
- Full integration suite green (176s)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker-compose.yml

@@ -86,6 +86,13 @@ services:
       GG_STRIPE_WEBHOOK_SECRET: ${GG_STRIPE_WEBHOOK_SECRET:-}
       GG_STRIPE_PRICE_PRO: ${GG_STRIPE_PRICE_PRO:-}
       GG_STRIPE_PRICE_BUSINESS: ${GG_STRIPE_PRICE_BUSINESS:-}
+      # Tier 2 Block D — branding image uploads. Stored on the named
+      # volume below so they survive container restarts; production
+      # would back this with S3 + CDN instead.
+      GG_UPLOADS_DIR: /var/lib/guestguard/uploads
+      GG_UPLOADS_PUBLIC_URL: http://localhost:8080/uploads
+    volumes:
+      - uploads-data:/var/lib/guestguard/uploads
     ports:
       - "8080:8080"
     depends_on:
@@ -154,3 +161,4 @@ services:
 volumes:
   postgres-data:
   nats-data:
+  uploads-data: