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_core/core__idb_dexie.ts

@@ -1,6 +1,53 @@
 import type { Dexie, Table } from 'dexie';
 import { browser } from '$app/environment';
 
+/**
+ * Checks IDB table content versions and clears any tables whose version has
+ * changed since the last check.
+ *
+ * Version numbers live in IDB_CONTENT_VERSIONS (store_versions.ts). State is
+ * tracked in localStorage (ae_idb_ver__{module}__{table}) so each table is
+ * cleared exactly once per version bump, not on every page load.
+ *
+ * Call once at module init in each db_*.ts, after the singleton is created.
+ * The clear is intentionally fire-and-forget — the SWR pattern repopulates
+ * from the API naturally after a cache miss.
+ *
+ * A null stored version (never tracked) is treated as outdated so existing
+ * installs with stale cached data are cleaned up on first run.
+ */
+export async function check_and_clear_idb_tables({
+    db_instance,
+    module_name,
+    table_versions,
+    log_lvl = 0
+}: {
+    db_instance: Dexie;
+    module_name: string;
+    table_versions: Record<string, number>;
+    log_lvl?: number;
+}): Promise<void> {
+    if (!browser) return;
+
+    for (const [table_name, expected_version] of Object.entries(table_versions)) {
+        const ls_key = `ae_idb_ver__${module_name}__${table_name}`;
+        const stored_raw = localStorage.getItem(ls_key);
+        const stored_version = stored_raw !== null ? parseInt(stored_raw, 10) : null;
+
+        if (stored_version === expected_version) continue;
+
+        try {
+            await db_instance.table(table_name).clear();
+            localStorage.setItem(ls_key, String(expected_version));
+            console.log(
+                `[IDB] "${module_name}.${table_name}" cleared — v${stored_version ?? 'new'} → v${expected_version}`
+            );
+        } catch (e) {
+            console.warn(`[IDB] Failed to clear "${module_name}.${table_name}":`, e);
+        }
+    }
+}
+
 /**
  * Extracts the primary key from an object using a prioritized list of possible key names.
  * @param obj The object to extract the ID from.