chore: remove dead TierPicker + strike resolved gotchas

TierPicker.vue is a 5-tier preset picker from before the arbitrary-
amount contribution redesign. Zero imports across app/ and server/ —
purely dead code (99 lines).

Strike two LAUNCH_READINESS bullets that describe already-fixed
issues: the "stale tier comment" in useMemberPayment.js (no `tier`
references remain in that file), and the SeriesPassPurchase auto-
refresh gotcha (fetchPassInfo() already runs after the success path
at line 318).

app/components/TierPicker.vue

@@ -1,99 +0,0 @@
-<template>
-  <div class="tier-picker">
-    <div
-      v-for="tier in tiers"
-      :key="tier.amount"
-      class="tier-option"
-      :class="{ current: modelValue === tier.amount }"
-      @click="$emit('update:modelValue', tier.amount)"
-    >
-      <span class="tier-amount">{{ tier.display }}</span>
-      <span v-if="tier.subtitle" class="tier-subtitle">{{ tier.subtitle }}</span>
-    </div>
-  </div>
-</template>
-
-<script setup>
-defineProps({
-  modelValue: { type: Number, default: 0 },
-  tiers: {
-    type: Array,
-    default: () => [
-      { amount: 0, display: "$0", label: "Free" },
-      { amount: 5, display: "$5", label: "/month" },
-      { amount: 15, display: "$15", label: "/month" },
-      { amount: 30, display: "$30", label: "/month" },
-      { amount: 50, display: "$50", label: "/month" },
-    ],
-  },
-});
-
-defineEmits(["update:modelValue"]);
-</script>
-
-<style scoped>
-.tier-picker {
-  display: flex;
-  gap: 0;
-  margin-bottom: 12px;
-}
-
-.tier-option {
-  flex: 1;
-  padding: 18px 8px;
-  text-align: center;
-  border: 1px dashed var(--border);
-  background: var(--bg);
-  cursor: pointer;
-  transition: all 0.15s;
-  position: relative;
-}
-
-/* Overlap adjacent borders so dashed lines collapse into one */
-.tier-option + .tier-option {
-  margin-left: -1px;
-}
-
-.tier-option:hover {
-  background: var(--surface-hover);
-}
-
-/* Active item paints its solid border on top of any neighbor */
-.tier-option.current {
-  border-color: var(--candle);
-  border-style: solid;
-  background: var(--surface);
-  z-index: 1;
-}
-
-.tier-amount {
-  font-size: 24px;
-  font-weight: 600;
-  color: var(--text);
-  font-family: "Brygada 1918", serif;
-  display: block;
-  line-height: 1.1;
-}
-
-.tier-option.current .tier-amount {
-  color: var(--candle);
-}
-
-.tier-subtitle {
-  display: block;
-  margin-top: 4px;
-  font-size: 11px;
-  color: var(--text-dim);
-  font-family: "Commit Mono", monospace;
-  letter-spacing: 0.02em;
-}
-
-@media (max-width: 768px) {
-  .tier-picker {
-    flex-wrap: wrap;
-  }
-  .tier-option {
-    min-width: 60px;
-  }
-}
-</style>