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>

frontend/pages/signup.vue

@@ -1,7 +1,17 @@
 <script setup lang="ts">
+// Sign-up page. Honors `?email=` (pre-fill) and `?redirect=` query params
+// so the collaborator-invite flow can hand a user from /invites/<token>
+// through signup → verify-email → login → back to /invites/<token>.
+// The redirect target survives across the verify-email round-trip via
+// sessionStorage (the verify link is server-generated and can't carry it
+// without a schema change).
 const auth = useAuth()
+const route = useRoute()
 
-const email = ref('')
+const email = ref(typeof route.query.email === 'string' ? route.query.email : '')
+const redirect = computed(() =>
+  typeof route.query.redirect === 'string' ? route.query.redirect : ''
+)
 const name = ref('')
 const password = ref('')
 const acceptTerms = ref(false)
@@ -14,6 +24,11 @@ async function submit() {
   submitting.value = true
   try {
     await auth.signup(email.value, name.value, password.value, acceptTerms.value)
+    // Park the desired post-verify destination so verify-email.vue can
+    // resume the flow once the inbox round-trip completes.
+    if (redirect.value && import.meta.client) {
+      sessionStorage.setItem('gg.postAuthRedirect', redirect.value)
+    }
     sent.value = true
   } catch (e: any) {
     error.value = useErrMessage(e, 'Sign-up failed')
@@ -21,6 +36,16 @@ async function submit() {
     submitting.value = false
   }
 }
+
+// Login link target. If we have a redirect carry it through; pre-fill the
+// email field too so the user doesn't retype it.
+const loginHref = computed(() => {
+  const q = new URLSearchParams()
+  if (email.value) q.set('email', email.value)
+  if (redirect.value) q.set('redirect', redirect.value)
+  const qs = q.toString()
+  return qs ? `/login?${qs}` : '/login'
+})
 </script>
 
 <template>
@@ -34,7 +59,7 @@ async function submit() {
         If <span class="text-zinc-200">{{ email }}</span> is reachable, we've sent a verification link.
         Click it to finish setting up your account.
       </p>
-      <NuxtLink to="/login" class="btn-ghost mt-4 w-full">Back to sign in</NuxtLink>
+      <NuxtLink :to="loginHref" class="btn-ghost mt-4 w-full">I've verified — sign in</NuxtLink>
     </div>
 
     <form v-else class="card space-y-4" @submit.prevent="submit">
@@ -84,7 +109,7 @@ async function submit() {
 
     <p class="mt-6 text-center text-sm text-zinc-400">
       Already have an account?
-      <NuxtLink to="/login" class="text-brand-400 hover:text-brand-300">Sign in</NuxtLink>
+      <NuxtLink :to="loginHref" class="text-brand-400 hover:text-brand-300">Sign in</NuxtLink>
     </p>
   </section>
 </template>