fix(bulk-edit): drop dead initial-* props and clear store on edit-mode discard

Felix B1 — `WhoWhenSection.svelte:37` and `DescriptionSection.svelte:42`
mutated $bindable props at top-level script scope, seeding them from
`initial*` companion props that no caller ever passes. The pattern stomps
parent-owned state in any future component re-evaluation.

Removed the dead initialDateIso / initialLocation / initialDocumentLocation
props and let the bindables carry their own initial value. dateDisplay and
currentTitle now seed from the bindable directly inside untrack — no
re-assignment required.

Elicit B2 — In edit mode the file map IS the user's bulk selection, so
discarding must clear bulkSelectionStore and bounce back to /documents,
otherwise the user is left on /documents/bulk-edit with an empty form
and a stale count in the bottom bar.

Refs #225, PR #331

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/document/WhoWhenSection.svelte

@@ -13,8 +13,6 @@ let {
 	senderId = $bindable(''),
 	selectedReceivers = $bindable<Person[]>([]),
 	dateIso = $bindable(''),
-	initialDateIso = '',
-	initialLocation = '',
 	initialSenderName = '',
 	suggestedDateIso = '',
 	suggestedSenderName = '',
@@ -24,8 +22,6 @@ let {
 	senderId?: string;
 	selectedReceivers?: Person[];
 	dateIso?: string;
-	initialDateIso?: string;
-	initialLocation?: string;
 	initialSenderName?: string;
 	suggestedDateIso?: string;
 	suggestedSenderName?: string;
@@ -33,8 +29,9 @@ let {
 	editMode?: boolean;
 } = $props();
 
-let dateDisplay = $state(untrack(() => isoToGerman(initialDateIso)));
-dateIso = untrack(() => initialDateIso);
+// Seed dateDisplay from the bindable's current value once at mount; subsequent
+// edits flow through handleDateInput which writes back to dateIso.
+let dateDisplay = $state(untrack(() => isoToGerman(dateIso)));
 let dateDirty = $state(false);
 
 const dateInvalid = $derived(dateDirty && dateDisplay.length > 0 && dateIso === '');
@@ -122,7 +119,6 @@ $effect(() => {
 					id="location"
 					type="text"
 					name="location"
-					value={initialLocation}
 					placeholder={m.form_placeholder_location()}
 					class="block w-full rounded border border-line px-2 py-3 text-sm shadow-sm focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
 				/>