chore(commons): use Headphones + Podcasts glyphs for the podcast tabs

Swaps PlayCircle / AudioFile (generic) for the canonical Material Symbols
podcast iconography — `headphones` (U+F01F) on the Episodes feed and
`podcasts` (U+F048, the mic + signal-waves glyph) on the Shows feed.
Both codepoints added to MaterialSymbols.kt and the subset font
regenerated via tools/material-symbols-subset/subset.sh.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/bottombars/NavBarItem.kt

@@ -252,14 +252,14 @@ val NavBarCatalog: Map<NavBarItem, NavBarItemDef> =
             NavBarItemDef(
                 id = NavBarItem.PODCAST_EPISODES,
                 labelRes = R.string.route_podcast_episodes,
-                icon = MaterialSymbols.PlayCircle,
+                icon = MaterialSymbols.Headphones,
                 resolveRoute = { Route.PodcastEpisodes },
             ),
         NavBarItem.PODCASTS to
             NavBarItemDef(
                 id = NavBarItem.PODCASTS,
                 labelRes = R.string.route_podcasts,
-                icon = MaterialSymbols.AudioFile,
+                icon = MaterialSymbols.Podcasts,
                 resolveRoute = { Route.Podcasts },
             ),
         NavBarItem.PUBLIC_CHATS to

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/icons/symbols/MaterialSymbols.kt

@@ -121,6 +121,7 @@ object MaterialSymbols {
     val Group = MaterialSymbol("\uEA21")
     val GroupAdd = MaterialSymbol("\uE7F0")
     val Groups = MaterialSymbol("\uF233")
+    val Headphones = MaterialSymbol("\uF01F")
     val Hearing = MaterialSymbol("\uE023")
     val History = MaterialSymbol("\uE8B3")
     val Home = MaterialSymbol("\uE9B2")
@@ -171,6 +172,7 @@ object MaterialSymbols {
     val PlayArrow = MaterialSymbol("\uE037")
     val PlayCircle = MaterialSymbol("\uE1C4")
     val PlayCircleOutline = MaterialSymbol("\uE1C4")
+    val Podcasts = MaterialSymbol("\uF048")
     val Poll = MaterialSymbol("\uF0CC")
     val PrivacyTip = MaterialSymbol("\uF0DC")
     val Public = MaterialSymbol("\uE80B")