fix(bridge): expose copy_from_cache_to_temp + harden launch_presentation

copy_from_cache_to_temp IPC handler was registered in file_handlers.ts
but never added to the preload bridge, making it unreachable from Svelte
despite being the documented preferred primitive for custom launch flows.

launch_presentation was the last handler still using osascript -e with
inline path injection. Converted to the temp-.scpt-file approach already
used by run_osascript and launch_from_cache — prevents breakage on
presentation filenames with spaces, quotes, or parentheses.

Also adds a pre-copy existence check to launch_from_cache so a missing
cache entry returns a meaningful error instead of a raw ENOENT.

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

dist/preload/index.js

@@ -14,6 +14,7 @@ electron_1.contextBridge.exposeInMainWorld('aetherNative', {
     open_local_file_v2: (path) => electron_1.ipcRenderer.invoke('native:open-local-file-v2', path),
     check_cache: (args) => electron_1.ipcRenderer.invoke('native:check-cache', args),
     download_to_cache: (args) => electron_1.ipcRenderer.invoke('native:download-to-cache', args),
+    copy_from_cache_to_temp: (args) => electron_1.ipcRenderer.invoke('native:copy-from-cache-to-temp', args),
     launch_from_cache: (args) => electron_1.ipcRenderer.invoke('native:launch-from-cache', args),
     launch_presentation: (args) => electron_1.ipcRenderer.invoke('native:launch-presentation', args),
     control_presentation: (args) => electron_1.ipcRenderer.invoke('native:control-presentation', args),