feat(schema): add bot_name and bot_icon to AgentDefaults (#3650)

Two new fields with safe defaults that preserve current branding:
- bot_name: str = "nanobot"
- bot_icon: str = "🐈"

Empty string for bot_icon is allowed and lets users opt out of the
leading icon. camelCase keys (botName, botIcon) bind via the existing
to_camel alias generator.

nanobot/config/schema.py

@@ -90,6 +90,8 @@ class AgentDefaults(Base):
     )  # Max characters for tool hint display (e.g. "$ cd …/project && npm test")
     reasoning_effort: str | None = None  # low / medium / high / adaptive - enables LLM thinking mode
     timezone: str = "UTC"  # IANA timezone, e.g. "Asia/Shanghai", "America/New_York"
+    bot_name: str = "nanobot"  # Display name shown in CLI prompts (e.g. "{name} is thinking...")
+    bot_icon: str = "🐈"  # Short icon (emoji or text) shown next to the bot name in CLI; "" to omit
     unified_session: bool = False  # Share one session across all channels (single-user multi-device)
     disabled_skills: list[str] = Field(default_factory=list)  # Skill names to exclude from loading (e.g. ["summarize", "skill-creator"])
     session_ttl_minutes: int = Field(