fix: Add UUID disambiguation for duplicate agent names

[szmania]

Summary

This PR enhances the TUI to provide better visibility into which agent is performing tasks, especially when multiple sub-agents are active. It also improves how status messages (spinners, confirmations, and errors) are attributed to specific agents using their UUIDs.

Changes

🤖 Agent Identification & Disambiguation

• Agent Name Resolution: Added logic in cecli/tui/app.py to resolve agent names from coder_uuid.
• Sub-agent Prefixing: TUI status messages (spinners, confirmations, and errors) now include the agent's name.
• Primary Agent Status: When sub-agents are present, the primary agent is identified as (primary) in the TUI.
• Duplicate Name Handling: If multiple sub-agents share the same name, they are disambiguated by appending the first 3 characters of their UUID (e.g., researcher (a1b)).

🔄 Improved Status Attribution

• UUID Propagation: Updated BaseCoder and TUI.IO to pass coder_uuid through spinner and other status updates. This ensures that TUI updates are correctly routed to the appropriate agent context.
• Enhanced TUI Components:
  • MainFooter now displays the active agent's name alongside the spinner.
  • StatusBar now prefixes notifications and confirmation prompts with the agent's name.

🛠️ Refactors & Fixes

• Utility Update: Replaced oslex.join with shlex.join in cecli/utils.py for better shell command escaping.
• Test Coverage: Added new TUI tests in tests/tui/test_app.py to verify agent name prefixing in various status message types.

Impact

Users will now have a clearer understanding of which agent is currently active and performing work in the TUI, improving the overall experience when using complex agentic workflows.