feedback5 WU: module type icons get one lower-case file per type (dec-X and dec-x were two names for one file)

The official data spells one DEC X module 'dec-X' (uniequip_003_aglina) and the others 'dec-x' (WAH-Y is the other
mixed-case type id), and the asset plan stored each under its own case: module/dec-X.png and module/dec-x.png. On
Windows / macOS those are one file, so a release zip built there could hold only one of them and a case-sensitive
server (a Linux VPS) would miss the other — the release packager found it ("planned but not staged"). The local file
is now module/{typeIcon in lower case}.png; the upstream names keep their order (the id as spelled, then lower case).

data/assets.json regenerated offline (node tools/fetch-assets.mjs --offline --add-only). JSON diff: modules.dec-X
/assets/module/dec-X.png -> /assets/module/dec-x.png, modules.WAH-Y /assets/module/WAH-Y.png -> /assets/module/wah-y.png,
hash, stats.files 6979 -> 6978, stats.bytes 458334505 -> 458333444; nothing else.

fetch-assets compares its orphans (what --prune deletes) without case: on Windows / macOS module/WAH-Y.png on disk is
the listed module/wah-y.png and must not be deleted (orphanFiles, exported).

Tests: test/assets-diy.test.js (one lower-case file per type, no two manifest URLs differing only in case, orphans).
docs/ASSETS.md: the module icon file name.

tools/assets/plan.mjs

@@ -595,8 +595,11 @@ export function buildPlan({ assets07, ops03, enemies05, maps05, audio, modelsDat
   // --- module type icons ----------------------------------------------------
   const modules = {};
   for (const t of [...new Set(moduleTypes || [])].filter((x) => typeof x === 'string' && /^[a-z0-9-]+$/i.test(x)).sort()) {
-    // the client's file name, else its lower-case form (the type id of a few modules is mixed case: WAH-Y → wah-y.png)
-    modules[t] = leaf(alt(`module/${safeName(t)}.png`, [...new Set([t, t.toLowerCase()])].map((n) => joinUrl(RAW.aa2, `arts/ui/uniequiptype/${n}.png`))));
+    // the client's file name, else its lower-case form (the type id of a few modules is mixed case: WAH-Y → wah-y.png).
+    // One lower-case file per type: the official data spells one DEC X module 'dec-X' (uniequip_003_aglina) and the
+    // others 'dec-x'; two paths that differ only in case are one file on Windows / macOS (and in a release zip built or
+    // extracted there), so a case-sensitive server would miss one of them.
+    modules[t] = leaf(alt(`module/${safeName(t).toLowerCase()}.png`, [...new Set([t, t.toLowerCase()])].map((n) => joinUrl(RAW.aa2, `arts/ui/uniequiptype/${n}.png`))));
   }
 
   // --- 干员战斗语音 (excel/charword_table.json → audio.voice) ---------------------------------------------