feat(rust): print the weapon name the module sends in the feed

PLAN.md M20 step 4. Module-Rust#60 gives every event frame a weaponName: the
game's own name for a ranged weapon, or the prefab name as words. The feed
printed the prefab name as words itself, which read "with ak47u entity".

weaponName() in RustFormat.kt is the Kotlin half of module-rust's format.js
weapon(). It prints frame.weaponName. Against a module too old to send it,
it drops the .entity / .weapon / .deployed ending before prefabName(), as
the website does, so an older module's kill reads "with ak47u".

Tests: a kill with weaponName, the same kill from an older module, and the
fallback's edges (blank name, each ending, an ending only at the end, no
weapon).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

app/src/main/java/com/runicgateway/app/ui/rust/RustFeed.kt

@@ -161,7 +161,7 @@ fun describe(row: RustEventDto): FeedLine {
  */
 private fun death(row: RustEventDto, name: String?): FeedLine {
     val where = listOfNotNull(
-        row.str("weapon")?.let { "with ${prefabName(it)}" },
+        row.str("weapon")?.let { "with ${weaponName(it, row.str("weaponName"))}" },
         row.num("distance")?.let { "${Math.round(it)}m" },
         row.str("grid"),
         if (row.flag("sleeping")) "while sleeping" else null,

app/src/main/java/com/runicgateway/app/ui/rust/RustFormat.kt

@@ -159,6 +159,23 @@ fun prefabName(name: String?): String {
     return name.replace(Regex("[_.]+"), " ").trim()
 }
 
+/** The endings a held entity's prefab name carries that no player says. */
+private val WEAPON_ENDING = Regex("[._](entity|weapon|deployed)$")
+
+/**
+ * The weapon in a kill, the Kotlin half of `module-rust`'s `format.js weapon()`.
+ * The module sends `weaponName` (Module-Rust#60), which is the game's own name for a
+ * gun or the prefab name as words (`server/model/titles/weaponNames.js`), and the
+ * app prints that. A module too old to send it gets the same fallback here: the
+ * `.entity` / `.weapon` / `.deployed` ending is dropped, then [prefabName] turns the
+ * rest into words. So the app never prints "ak47u entity".
+ */
+fun weaponName(weapon: String?, weaponName: String?): String {
+    if (weapon.isNullOrBlank()) return ""
+    if (!weaponName.isNullOrBlank()) return weaponName
+    return prefabName(weapon.trim().replace(WEAPON_ENDING, ""))
+}
+
 /**
  * An Economics balance (`docs/modules/rust/PLAN_REDESIGNS.md` §11.2.2): grouped,
  * at most two places, and a dash for one the server never reported — not "0",