fix(history): bulk delete + clear-all now persist to SQLite

The Phase 9 bulk-delete path passed UUID strings to deleteFromHistory(index),
which expected an integer; JS coerced the string to NaN and splice(NaN, 1)
collapsed to splice(0, 1), so bulk-delete silently removed the first N visible
rows instead of the selected ones, then fired delete_transcript against the
wrong IDs.

Clear-all called saveHistory(), which was a no-op stub left over from the
same incomplete-refactor pattern that produced the manualTags persistence bug
fixed in 7eb52d9. The in-memory array was emptied, but SQLite still held
every transcript, so they reappeared on next loadHistory().

- Add deleteFromHistoryById(id) next to the index-keyed deleteFromHistory.
- bulkDelete now calls deleteFromHistoryById.
- clearAll now awaits an explicit per-id delete loop and surfaces a toast on
  partial failure.
- Remove the saveHistory() stub and its sole caller's import.

https://claude.ai/code/session_0189xUb6ie6t9qHkzatGZ9Rb

src/lib/stores/page.svelte.ts

@@ -223,8 +223,6 @@ if (typeof window !== "undefined" && hasTauriRuntime()) {
   loadHistory().catch(() => {});
 }
 
-export function saveHistory() {}
-
 export async function addToHistory(entry: TranscriptWriteEntry) {
   const normalised = normaliseTranscriptEntry(entry);
   history.unshift(normalised);
@@ -323,6 +321,12 @@ export function deleteFromHistory(index: number) {
     .catch((err) => console.warn("deleteFromHistory: SQLite delete failed", err));
 }
 
+export function deleteFromHistoryById(id: string) {
+  const idx = history.findIndex((entry) => String(entry.id) === String(id));
+  if (idx === -1) return;
+  deleteFromHistory(idx);
+}
+
 export const tasks = $state<TaskEntry[]>([]);
 
 function mapTaskRow(row: TaskDto): TaskEntry {