m4.5: inline #tags — hashtags in a note become labels (two-way sync)

Fast, cross-device labelling: type #groceries in a note and it becomes
the "groceries" label. The body is the source of truth for tag-labels;
manual picker labels stay independent (rule 28 — additive).

- note_labels.via_tag (migration 0013) marks tag-sourced attachments.
- parse_tags(): #tag at start-of-body or after whitespace, needs a
  letter (so #2024, URL #frags, mid#word are ignored). unit-tested.
- _reconcile_tags() on create + body-update: attach labels for current
  #tags (find-or-create, case-insensitive), detach tag-labels whose tag
  was removed; never touches manual (via_tag=false) rows.
- label picker (set_note_labels + editor onLabelsChange) now preserves
  tag-labels on save, so a picker action can't strip a label the #tag
  still mandates.
- serialize via_tag; card/editor chips render tag-labels as "#name",
  and the editor hides the × on them (remove by editing the tag text).
- LabelPicker builds manual NoteLabels (via_tag:false).

Fourth and final item of M4.5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/LabelPicker.vue

@@ -1,9 +1,12 @@
 <script setup lang="ts">
 import { computed, onBeforeUnmount, onMounted, ref } from "vue";
-import { useLabelsStore } from "../stores/labels";
+import { useLabelsStore, type Label } from "../stores/labels";
 import Icon from "./Icon.vue";
 import type { NoteLabel } from "../stores/notes";
 
+// A label attached via the picker is manual (via_tag: false).
+const asManual = (lb: Label): NoteLabel => ({ id: lb.id, name: lb.name, color: lb.color, via_tag: false });
+
 const props = defineProps<{ modelValue: NoteLabel[] }>();
 const emit = defineEmits<{ (e: "update:modelValue", value: NoteLabel[]): void }>();
 const labels = useLabelsStore();
@@ -21,17 +24,17 @@ const canCreate = computed(() => {
   return name.length > 0 && !labels.items.some((lb) => lb.name.toLowerCase() === name.toLowerCase());
 });
 
-function toggle(lb: NoteLabel) {
+function toggle(lb: Label) {
   const next = selectedIds.value.has(lb.id)
     ? props.modelValue.filter((x) => x.id !== lb.id)
-    : [...props.modelValue, lb];
+    : [...props.modelValue, asManual(lb)];
   emit("update:modelValue", next);
 }
 
 async function createAndAdd() {
   const created = await labels.create(filter.value.trim());
   filter.value = "";
-  if (!selectedIds.value.has(created.id)) emit("update:modelValue", [...props.modelValue, created]);
+  if (!selectedIds.value.has(created.id)) emit("update:modelValue", [...props.modelValue, asManual(created)]);
 }
 
 function onDocMousedown(e: MouseEvent) {