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

AGENTS.md

@@ -235,6 +235,7 @@ hermes_cli/skin_engine.py    # SkinConfig dataclass, built-in skins, YAML loader
 | Spinner verbs | `spinner.thinking_verbs` | `display.py` |
 | Spinner wings (optional) | `spinner.wings` | `display.py` |
 | Tool output prefix | `tool_prefix` | `display.py` |
+| Per-tool emojis | `tool_emojis` | `display.py` → `get_tool_emoji()` |
 | Agent name | `branding.agent_name` | `banner.py`, `cli.py` |
 | Welcome message | `branding.welcome` | `cli.py` |
 | Response box label | `branding.response_label` | `cli.py` |