fix(vite): guard cleanStaleChunks — vp test deleted every built chunk

The cleanStaleChunks plugin lives in the shared vite config, so its
closeBundle hook also fired under `vp test` — where generateBundle never
runs, produced stayed empty, and the sweep deleted every hashed chunk
in web/static (28 files → 3). The entries still referenced their old
imports, so every page 404'd and Alpine never started: the whole reader
and media system appeared dead after merely running the test suite.

Guard: skip the sweep when produced.size === 0 — not a build run, no
build output to clean. Verified: build → 28 files, test → 28 files;
back-to-back builds stay byte-identical.

vite.config.ts

@@ -19,6 +19,13 @@ const pdfjsAssets = () => ({
 // so hashed chunks from previous builds would otherwise accumulate
 // forever and leak into Docker images via the build context. Remove
 // any *-<hash>.js/.css/.mjs(.map) that this build did not produce.
+//
+// The produced.size === 0 guard is load-bearing: this config also drives
+// `vp test`, and vitest runs closeBundle with generateBundle never having
+// fired — an empty produced set means "not a build run", and sweeping
+// then deleted every live chunk (the 2026-10-21 incident where
+// `npm run test` gutted web/static down to the three entry files and
+// every page 404'd its imports).
 const cleanStaleChunks = () => {
   const produced = new Set<string>();
   return {
@@ -27,6 +34,7 @@ const cleanStaleChunks = () => {
       for (const fileName of Object.keys(bundle)) produced.add(fileName);
     },
     closeBundle() {
+      if (produced.size === 0) return;
       const outDir = "web/static";
       const chunkRe = /-[A-Za-z0-9_-]{8}\.(js|css|mjs)(\.map)?$/;
       for (const f of readdirSync(outDir)) {