Per-tool emoji on tool cards (gateway-resolved via hermes get_tool_emoji)

tool.start gains an optional cosmetic 'emoji' field, resolved server-side
through hermes' own display layer (active-skin overrides, then the tool
registry's per-tool emoji) so icons track the user's hermes theme and
new/plugin tools get their glyph for free. Omitted for unknown tools so
the app falls back to its default wrench.

- protocol.py: tool_start(emoji=...) kwarg, payload field when set
- adapter.py: _tool_emoji() helper (lazy import, None on unknown/failure)
- frames.schema.json + docs/04: field documented
- app: ToolStartPayload.emoji -> ToolItem.emoji -> ToolCard header
- tests: frame shape, resolution/fallback, end-to-end tool.start emoji

app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt

@@ -103,6 +103,9 @@ data class ToolItem(
     val name: String,
     val preview: String? = null,
     val args: JsonElement? = null,
+    /** Cosmetic per-tool glyph from the gateway (hermes get_tool_emoji);
+     *  null for unknown tools / older frames — the UI falls back to 🔧. */
+    val emoji: String? = null,
     val note: String? = null,
     val done: Boolean = false,
     val ok: Boolean = true,
@@ -450,6 +453,7 @@ class ChatStore {
                     name = p.name,
                     preview = p.preview,
                     args = p.args,
+                    emoji = p.emoji,
                     anchorId = anchorId,
                 )
         }

app/shared/src/commonMain/kotlin/iris/protocol/Protocol.kt

@@ -271,6 +271,9 @@ data class ToolStartPayload(
     val name: String,
     val preview: String? = null,
     val args: JsonElement? = null,
+    /** Cosmetic per-tool glyph resolved server-side (hermes get_tool_emoji);
+     *  absent for unknown tools — the UI falls back to its default. */
+    val emoji: String? = null,
 )
 
 @Serializable

app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt

@@ -2767,7 +2767,7 @@ private fun ToolCard(
                 Spacer(modifier = Modifier.width(6.dp))
             }
             Text(
-                "🔧 ${tool.name}",
+                "${tool.emoji ?: "🔧"} ${tool.name}",
                 fontSize = 13.sp,
                 fontWeight = FontWeight.Medium,
                 color = IrisColors.textBright,