feat: add global unified context mode with UMO restoration for cross-platform conversation continuity

[Copilot]

Implements global unified context mode allowing all platforms/sessions to share a single conversation history while maintaining platform awareness and proper message routing.

Changes

Configuration

• Added platform_settings.global_unified_context_mode (default: false)
• Constants: GLOBAL_UNIFIED_CONTEXT_UMO = "global::global" for shared context identifier and ORIGINAL_UMO_KEY = "original_umo" for consistent key usage

WakingCheckStage (pipeline/waking_check/stage.py)

• Replaces event UMO with constant when mode enabled
• Stores original UMO in event extras for downstream use

MainAgent (astr_main_agent.py)

• Injects platform context into user prompts when global UMO detected
• Format: [Context: Platform={id}, Type={type}, Session={session}] {user_message}

RespondStage (pipeline/respond/stage.py)

• Restores original UMO before sending messages (both regular and streaming)
• Ensures messages are delivered to the correct original session

SendMessageToUserTool (astr_main_agent_resources.py)

• Defaults to original UMO when in global context mode
• Added session parameter to tool schema for explicit session targeting
• LLM can send messages to specific sessions using format: platform:type:session_id

Dashboard Theme (dashboard/src/theme/DarkTheme.ts)

• Updated dark theme color scheme to match light theme
• Primary: #3c96ca, Secondary: #2288b7

Behavior

# Normal mode: separate contexts per session
qq:group:123456    → conversation A
telegram:private:789 → conversation B

# Global mode: shared context with platform tags and UMO restoration
qq:group:123456    → global::global (for context) + "[Context: Platform=qq, Type=group, Session=123456] ..."
                   → qq:group:123456 (restored for message delivery)
telegram:private:789 → global::global (for context) + "[Context: Platform=telegram, Type=private, Session=789] ..."
                     → telegram:private:789 (restored for message delivery)

LLM maintains continuity across platforms while understanding message origin through injected context tags. Messages are correctly routed to original sessions through UMO restoration.

Original prompt

帮我增加 全局统一上下文模式，增加一个配置项：是否启用 。在waking 阶段识别到是全局上下文，就直接改umo为一个常量。在internal.py如果识别到umo是全局上下文，就加一些user prompt，比如平台id 什么的辅助llm理解。

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[Soulter]

@copilot 还得把send message to user增加一个umo参数（或者新增一个tool，带有这个参数，这会很好） 会通过这个tool来发送消息。此外，需要预先备份好原来的umo，在respond stage发送前恢复，以及send streaming那里

[Copilot]

@copilot 还得把send message to user增加一个umo参数（或者新增一个tool，带有这个参数，这会很好） 会通过这个tool来发送消息。此外，需要预先备份好原来的...

Done in commit 3091b92. Changes made:

1. RespondStage: Restores original UMO before sending messages (both regular and streaming)
2. SendMessageToUserTool:
   • Now defaults to original UMO when in global context mode
   • Added session parameter to tool schema so LLM can explicitly specify target session
   • Tool can send to any session using the session parameter format: platform:type:session_id

The UMO is backed up in WakingCheckStage and restored in RespondStage before all send operations, ensuring messages are delivered to the correct original session.