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>

internal/domain/branding.go

@@ -0,0 +1,73 @@
+package domain
+
+import (
+	"errors"
+	"regexp"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// Branding is one event's visual customisation. All fields are optional —
+// a brand-new event renders with the GuestGuard defaults until the host
+// fills any of these in. Tier 2 Block D.
+type Branding struct {
+	EventID         uuid.UUID `json:"event_id"`
+	PrimaryColor    *string   `json:"primary_color,omitempty"`
+	AccentColor     *string   `json:"accent_color,omitempty"`
+	LogoURL         *string   `json:"logo_url,omitempty"`
+	CoverImageURL   *string   `json:"cover_image_url,omitempty"`
+	FontFamily      *string   `json:"font_family,omitempty"`
+	GreetingMessage *string   `json:"greeting_message,omitempty"`
+	UpdatedAt       time.Time `json:"updated_at"`
+}
+
+// AllowedFonts is the curated picker list the host can choose from. Locking
+// it down keeps render times sane (no hot-loading arbitrary @font-face
+// files) and avoids smuggling untrusted CSS into our emails.
+var AllowedFonts = []string{
+	"Inter",
+	"Playfair Display",
+	"Cormorant Garamond",
+	"Lora",
+	"DM Sans",
+	"Manrope",
+}
+
+// IsAllowedFont reports whether `f` is in the curated set. Empty string is
+// fine — the RSVP page falls back to its default.
+func IsAllowedFont(f string) bool {
+	if f == "" {
+		return true
+	}
+	for _, a := range AllowedFonts {
+		if f == a {
+			return true
+		}
+	}
+	return false
+}
+
+// hexColorRe matches #abc, #abcd, #aabbcc, #aabbccdd (alpha optional).
+// Lowercase + uppercase OK. Length checked because Go regexp + Postgres
+// don't agree on Unicode digits and we want plain ASCII here.
+var hexColorRe = regexp.MustCompile(`^#([0-9A-Fa-f]{3,8})$`)
+
+// IsValidHexColor accepts the three common hex shorthand forms. Empty is OK
+// (clears the column).
+func IsValidHexColor(c string) bool {
+	if c == "" {
+		return true
+	}
+	if !hexColorRe.MatchString(c) {
+		return false
+	}
+	n := len(c) - 1
+	return n == 3 || n == 4 || n == 6 || n == 8
+}
+
+var (
+	ErrBrandingNotFound = errors.New("branding not found")
+	ErrInvalidColor     = errors.New("color must be a hex value (e.g. #22c55e)")
+	ErrUnknownFont      = errors.New("font is not in the allowlist")
+)