feat(tui): --connect mode to attach TUI to remote daemon via A2A SSE

[bug-ops]

Parent

Part of #581. Depends on streaming TaskProcessor and --daemon issues.

Summary

Add --connect <url> CLI flag that starts TUI in remote mode: connects to a running daemon's A2A endpoint, sends user messages, renders streaming SSE responses token-by-token.

Scope

Files: src/main.rs, crates/zeph-tui/src/lib.rs (minor)

CLI flag

#[cfg(all(feature = "tui", feature = "a2a"))]
#[arg(long, value_name = "URL")]
connect: Option<String>,

run_tui_remote(url, auth_token) function

1. Create A2aClient with ssrf_protection=false, require_tls=false (localhost)
2. Generate context_id = Uuid::new_v4() for session continuity
3. Build TUI App with standard mpsc channels
4. SSE pump task: for each user input from user_rx:
   • Build SendMessageParams with message.context_id
   • Call client.stream_message() → TaskEventStream
   • Map SSE events to AgentEvent:
     • ArtifactUpdate(text, !is_final) → AgentEvent::Chunk
     • StatusUpdate(Working) → AgentEvent::Typing
     • StatusUpdate(Completed) → AgentEvent::Flush
     • StatusUpdate(Failed) → AgentEvent::FullMessage("Error: ...")
5. No changes to App rendering — it already handles AgentEvent

Acceptance Criteria

• cargo run --features tui,a2a -- --connect http://localhost:8080 connects to daemon
• User input sent as A2A messages, responses streamed token-by-token
• Multi-turn conversation works (context persists via context_id)
• Connection error shown gracefully in TUI
• Ctrl-C exits TUI cleanly