perf(frontend): virtualize ResourceList rows (list view)

Large folders/collections rendered every row into the DOM, so memory and
scripting time grew linearly with item count. A 20k-row list took ~12.5s to
first paint, held ~380k DOM nodes / ~281MB JS heap, and scrolled at ~4fps.

Add a reusable, dependency-free `VirtualList` that windows rows against the
nearest scrollable ancestor (the existing `.content-area`), so the
single-scrollbar UX, sticky header and end-of-list sentinel are unchanged. It
reserves the full scroll height with a sized spacer and translates a small
window of rows; row height is auto-measured for the single-column case.

Wire it into ResourceList's flat list view (recent, favorites, shared,
shared-with-me, trash, search). Grouped sections and grid view are unchanged
for now and are the next callers of the same primitive.

Measured in headless Chromium (1280x900) with synthetic rows, before/after:

  rows  | mount→paint | DOM nodes | JS heap | scroll frame | jank frames
  ------+-------------+-----------+---------+--------------+------------
   1000 | 632→70 ms   | 19k→351   | 16→2 MB | 17→17 ms     | 0→0
   5000 | 4401→54 ms  | 95k→351   | 72→3 MB | 47→17 ms     | 136→0
  20000 | 12577→56 ms | 380k→351  |281→6 MB |258→17 ms     | 1443→0

Rendered DOM and heap are now flat (O(visible)) regardless of dataset size;
scroll holds 60fps with zero jank. Correctness verified by probing a mid-list
scroll (rows land at the expected indices, positioned within the viewport).

eslint: disable core `no-undef` for `.svelte` (TypeScript/svelte-check already
resolve identifiers, including `<script generics>` type params it can't see).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M8Vb9QHmLZnEMzHz7MrFy6

frontend/eslint.config.js

@@ -24,11 +24,16 @@ export default ts.config(
 			parserOptions: {
 				parser: ts.parser
 			}
+		},
+		// TypeScript + svelte-check already resolve identifiers (including `<script
+		// generics>` type params, which core `no-undef` can't see). Defer to them.
+		rules: {
+			'no-undef': 'off'
 		}
 	},
 	{
 		// `static/` holds vendored, verbatim assets (the delta-upload worker and
 		// the wasm-bindgen hash glue) — lint them as the upstream ships them.
-		ignores: ['build/', '.svelte-kit/', 'package/', 'static/']
+		ignores: ['build/', '.svelte-kit/', 'package/', 'static/', 'bench/']
 	}
 );