feat(idb): add IDB content version check system, wire to journals

Adds check_and_clear_idb_tables() helper in core__idb_dexie.ts that clears
Dexie tables when their content version changes. Version numbers live in
IDB_CONTENT_VERSIONS (store_versions.ts); state tracked in localStorage
(ae_idb_ver__{module}__{table}) so each table clears exactly once per bump.

Wired into db_journals.ts (pilot): journal_entry at v3 clears stale
content_md_html/history_md_html data cached before the properties_to_save fix.

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

src/lib/ae_journals/db_journals.ts

@@ -1,7 +1,10 @@
 import Dexie, { type Table } from 'dexie';
+import { browser } from '$app/environment';
 
 import type { key_val } from '$lib/stores/ae_stores';
 import type { ae_Journal, ae_JournalEntry } from '$lib/types/ae_types';
+import { IDB_CONTENT_VERSIONS } from '$lib/stores/store_versions';
+import { check_and_clear_idb_tables } from '$lib/ae_core/core__idb_dexie';
 
 // li = list
 // kv = key value list
@@ -141,3 +144,14 @@ export class MySubClassedDexie extends Dexie {
 }
 
 export const db_journals = new MySubClassedDexie();
+
+// On each page load, clear any tables whose content version has changed.
+// Versions are defined in store_versions.ts IDB_CONTENT_VERSIONS.journals.
+// Each table is only cleared once per version bump (tracked in localStorage).
+if (browser) {
+    check_and_clear_idb_tables({
+        db_instance: db_journals,
+        module_name: 'journals',
+        table_versions: IDB_CONTENT_VERSIONS.journals
+    }).catch((e) => console.warn('[db_journals] IDB version check failed:', e));
+}