feat(tools): centralize tool emoji metadata in registry + skin integration

- Add 'emoji' field to ToolEntry and 'get_emoji()' to ToolRegistry
- Add emoji= to all 50+ registry.register() calls across tool files
- Add get_tool_emoji() helper in agent/display.py with 3-tier resolution:
  skin override → registry default → hardcoded fallback
- Replace hardcoded emoji maps in run_agent.py, delegate_tool.py, and
  gateway/run.py with centralized get_tool_emoji() calls
- Add 'tool_emojis' field to SkinConfig so skins can override per-tool
  emojis (e.g. ares skin could use swords instead of wrenches)
- Add 11 tests (5 registry emoji, 6 display/skin integration)
- Update AGENTS.md skin docs table

Based on the approach from PR #1061 by ForgingAlex (emoji centralization
in registry). This salvage fixes several issues from the original:
- Does NOT split the cronjob tool (which would crash on missing schemas)
- Does NOT change image_generate toolset/requires_env/is_async
- Does NOT delete existing tests
- Completes the centralization (gateway/run.py was missed)
- Hooks into the skin system for full customizability

agent/display.py

@@ -59,6 +59,32 @@ def get_skin_tool_prefix() -> str:
     return "┊"
 
 
+def get_tool_emoji(tool_name: str, default: str = "⚡") -> str:
+    """Get the display emoji for a tool.
+
+    Resolution order:
+    1. Active skin's ``tool_emojis`` overrides (if a skin is loaded)
+    2. Tool registry's per-tool ``emoji`` field
+    3. *default* fallback
+    """
+    # 1. Skin override
+    skin = _get_skin()
+    if skin and skin.tool_emojis:
+        override = skin.tool_emojis.get(tool_name)
+        if override:
+            return override
+    # 2. Registry default
+    try:
+        from tools.registry import registry
+        emoji = registry.get_emoji(tool_name, default="")
+        if emoji:
+            return emoji
+    except Exception:
+        pass
+    # 3. Hardcoded fallback
+    return default
+
+
 # =========================================================================
 # Tool preview (one-line summary of a tool call's primary argument)
 # =========================================================================