fix: extend poster session type context to all file list wrapper contexts

element_manage_event_file_li_all.svelte — also derives context_session_type_code
via Dexie chain (event_presentation → session, or event_presenter → presentation →
session) and passes it to element_manage_event_file_li. Fixes the button not showing
when viewing a presenter's files from the session view.

element_manage_event_file_li_direct.svelte — extends the Dexie chain to also handle
event_session (direct lookup) and event_presentation, not just event_presenter.

Both: correct API URL to /v3/hosted_file/ per backend agent's examples.

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

src/routes/events/ae_comp__event_file_obj_tbl.svelte

@@ -87,7 +87,7 @@
                 || event_file_obj.event_presentation_id
                 || event_file_obj.event_id;
             const filename_no_ext = (event_file_obj.filename ?? 'poster_image').replace(/\.pdf$/i, '');
-            const url = `${$ae_api.base_url}/v3/action/hosted_file/${event_file_obj.hosted_file_id}/convert_file`
+            const url = `${$ae_api.base_url}/v3/hosted_file/${event_file_obj.hosted_file_id}/convert_file`
                 + `?link_to_type=${encodeURIComponent(link_to_type)}`
                 + `&link_to_id=${encodeURIComponent(link_to_id)}`
                 + `&filename_no_ext=${encodeURIComponent(filename_no_ext)}`