Chat tabs, chat mode, own modes, compaction notice, CLI binaries again

- Terminals and file managers as tabs of a chat; chat terminals keep running on
  the server (no idle timeout) and re-attach from any device
- "Just chat" in New session and a built-in chat mode with a lean prompt and only
  web tools; custom modes with kind (coding/conversation), read-only and tool picker
- Mode selector as a dropdown
- The chat shows running compactions (automatic: tokens and share of the limit)
  and labels summaries
- Docker image builds and serves the terminal client binaries again
- Fix: atomic session updates; background title/usage writes no longer undo each
  other (auto compaction triggered one turn late)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/config.rs

@@ -385,6 +385,13 @@ pub struct AgentConfig {
     pub tools: Option<Vec<String>>,
     #[serde(default)]
     pub prompt: Option<String>,
+    /// Only read-only tools (like plan mode).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub read_only: Option<bool>,
+    /// "coding" (default: project context and coding instructions) or "chat" (plain
+    /// conversation with only this prompt, like the built-in chat mode).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub style: Option<String>,
     /// Max. instances of this subagent running at the same time.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub max_parallel: Option<usize>,