feat(projects): list + create API and creatable ProjectAutocomplete (T4)

- GET /api/projects returns the shared global list; POST /api/projects
  creates a project, deduped case-insensitively (F3).
- Repository find-or-create trims and matches on lower(name); a unique index
  on lower(name) enforces the same rule at the DB (replacing the case-
  sensitive column unique constraint) — migration 0001.
- ProjectAutocomplete: creatable autocomplete that lists projects, offers to
  create an unknown name inline, and selects it without reload.
- Integration test (dedupe/list against Postgres) + component test.

app/components/ProjectAutocomplete.vue

@@ -0,0 +1,148 @@
+<script setup lang="ts">
+// Creatable autocomplete over the shared global project list (C4, F3): pick an
+// existing project or persist a new one inline, deduped case-insensitively.
+interface Project {
+  id: string
+  name: string
+}
+
+const props = defineProps<{ modelValue?: Project | null }>()
+const emit = defineEmits<{ 'update:modelValue': [Project | null] }>()
+
+const projects = ref<Project[]>([])
+const query = ref(props.modelValue?.name ?? '')
+const open = ref(false)
+const busy = ref(false)
+
+onMounted(async () => {
+  projects.value = await $fetch<Project[]>('/api/projects')
+})
+
+const filtered = computed(() => {
+  const q = query.value.trim().toLowerCase()
+  if (!q) return projects.value
+  return projects.value.filter((p) => p.name.toLowerCase().includes(q))
+})
+
+// Case-insensitive: typing "acme" when "Acme" exists is not a new project.
+const exactMatch = computed(() => {
+  const q = query.value.trim().toLowerCase()
+  return projects.value.find((p) => p.name.toLowerCase() === q)
+})
+
+const canCreate = computed(() => query.value.trim().length > 0 && !exactMatch.value)
+
+function select(project: Project) {
+  query.value = project.name
+  open.value = false
+  emit('update:modelValue', project)
+}
+
+async function create() {
+  const name = query.value.trim()
+  if (!name || busy.value) return
+  busy.value = true
+  try {
+    const project = await $fetch<Project>('/api/projects', {
+      method: 'POST',
+      body: { name },
+    })
+    if (!projects.value.some((p) => p.id === project.id)) {
+      projects.value.push(project)
+    }
+    select(project)
+  } finally {
+    busy.value = false
+  }
+}
+</script>
+
+<template>
+  <div class="project-autocomplete">
+    <input
+      v-model="query"
+      type="text"
+      class="input"
+      data-test="project-input"
+      placeholder="Project…"
+      autocomplete="off"
+      @focus="open = true"
+      @input="open = true"
+    >
+    <ul v-if="open && (filtered.length || canCreate)" class="options">
+      <li v-for="project in filtered" :key="project.id">
+        <button
+          type="button"
+          class="option"
+          data-test="project-option"
+          :data-project-id="project.id"
+          @click="select(project)"
+        >
+          {{ project.name }}
+        </button>
+      </li>
+      <li v-if="canCreate">
+        <button
+          type="button"
+          class="option option--create"
+          data-test="project-create"
+          :disabled="busy"
+          @click="create"
+        >
+          + Create “{{ query.trim() }}”
+        </button>
+      </li>
+    </ul>
+  </div>
+</template>
+
+<style scoped>
+.project-autocomplete {
+  position: relative;
+  font-family: 'Cutive Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+}
+
+.input {
+  width: 100%;
+  border: 1px dashed currentColor;
+  background: transparent;
+  font: inherit;
+  padding: 0.4rem 0.5rem;
+  box-sizing: border-box;
+}
+
+.options {
+  position: absolute;
+  z-index: 1;
+  left: 0;
+  right: 0;
+  margin: 0.25rem 0 0;
+  padding: 0;
+  list-style: none;
+  border: 1px solid currentColor;
+  background: var(--surface, #fff);
+  max-height: 12rem;
+  overflow-y: auto;
+}
+
+.option {
+  display: block;
+  width: 100%;
+  border: 0;
+  background: transparent;
+  font: inherit;
+  text-align: left;
+  cursor: pointer;
+  padding: 0.4rem 0.5rem;
+}
+
+.option:hover,
+.option:focus {
+  outline: 1px solid currentColor;
+}
+
+.option--create {
+  opacity: 0.85;
+  font-style: italic;
+}
+</style>