feat(upload): skip unreadable files (FIFOs/sockets) + auto-reload on new deploy

Two robustness fixes behind the recurring "folder upload stuck at ~93%" reports.

1. Skip non-regular files up front. A copied s6/runit service tree contains
   FIFOs (e.g. supervise/control named pipes) that report a size but BLOCK
   FOREVER when the browser reads them — the deterministic ~8-files-short that
   no retry/watchdog tweak could fix. uploadBatch/uploadTree now probe each
   file's first chunk against a 3 s timeout (partitionReadable), upload only the
   readable ones, and report the rest: "N uploaded · M skipped (not regular
   files)". Progress runs over the uploadable count, so it reaches 100% instead
   of parking at 93% while a lane hangs on a pipe.

2. Auto-reload on a new deploy. svelte.config.js polls _app/version.json
   (60 s); the root layout reloads itself when the deployed build changes —
   unless an upload is in flight — so an open tab can't keep running stale code
   after a rebuild (the recurring "my fix isn't applied" trap).

npm run check: 0 errors, 58 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/svelte.config.js

@@ -30,6 +30,12 @@ const config = {
 		// All routes are client-rendered; SSR/prerender are disabled in +layout.ts.
 		alias: {
 			$lib: './src/lib'
+		},
+		// Poll `_app/version.json` so an open tab notices a fresh deploy; the root
+		// layout reloads itself when it does, instead of silently running stale
+		// code after a rebuild (the classic "my fix isn't applied" trap).
+		version: {
+			pollInterval: 60000
 		}
 	}
 };