Remove _random ID references and fix hosted file download ID

- Fix download button to use hosted_file_id instead of id (which resolved
  to event_file_id via _process_generic_props, hitting the wrong endpoint)
- Fix Dexie file table query in event_file_obj_tbl_wrapper to use _id
  fields (the indexed ones) instead of _id_random variants
- Remove _random fields from properties_to_save in event, event_session
- Drop _id_random fallbacks from launcher device ID resolution and
  background sync heartbeat
- Clean up dead comments and old FA anchor in post edit component
- Update TODO__Agents.md: BGH section removed, CMSC/Axonius shows added,
  download button fix marked complete

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

src/lib/ae_core/ae_comp__hosted_files_download_button.svelte

@@ -128,10 +128,7 @@ $effect(() => {
 let ae_promises: key_val = $state({});
 
 $effect(() => {
-    const file_id =
-        hosted_file_obj?.id ||
-        hosted_file_obj?.hosted_file_id ||
-        hosted_file_id;
+    const file_id = hosted_file_obj?.hosted_file_id ?? hosted_file_id;
     if (file_id && $ae_sess?.api_download_kv[file_id]?.percent_completed) {
         download_percent = $ae_sess.api_download_kv[file_id].percent_completed;
     }
@@ -139,10 +136,7 @@ $effect(() => {
 
 // Reactive timer to alternate views during active download
 $effect(() => {
-    const file_id =
-        hosted_file_obj?.id ||
-        hosted_file_obj?.hosted_file_id ||
-        hosted_file_id;
+    const file_id = hosted_file_obj?.hosted_file_id ?? hosted_file_id;
     const is_actively_downloading =
         ae_promises[file_id] && download_complete === undefined;
 
@@ -193,10 +187,7 @@ let direct_download_url = $derived.by(() => {
 });
 
 async function handle_click() {
-    const file_id =
-        hosted_file_obj?.id ||
-        hosted_file_obj?.hosted_file_id ||
-        hosted_file_id;
+    const file_id = hosted_file_obj?.hosted_file_id ?? hosted_file_id;
     download_complete = undefined;
     download_status_msg = 'Downloading...';
 
@@ -238,10 +229,7 @@ async function handle_click() {
 </script>
 
 {#snippet content()}
-    {@const file_id =
-        hosted_file_obj?.id ||
-        hosted_file_obj?.hosted_file_id ||
-        hosted_file_id}
+    {@const file_id = hosted_file_obj?.hosted_file_id ?? hosted_file_id}
     {#await ae_promises[file_id]}
         <div class="flex min-h-[1.5rem] w-full items-center">
             <div
@@ -316,8 +304,7 @@ async function handle_click() {
 {/snippet}
 
 {#if hosted_file_id && hosted_file_obj}
-    {@const file_id =
-        hosted_file_obj.id || hosted_file_obj.hosted_file_id || hosted_file_id}
+    {@const file_id = hosted_file_obj.hosted_file_id ?? hosted_file_id}
 
     {#if show_direct_download}
         <a