Revert to tokio::sync::Mutex, fix lock-across-await bugs, move input ownership to InteractScreen

The std::sync::Mutex detour caught every place a MutexGuard lived
across an await point in Agent::turn — the compiler enforced Send
safety that tokio::sync::Mutex silently allows. With those fixed,
switch back to tokio::sync::Mutex (std::sync blocks tokio worker
threads and panics inside the runtime).

Input and command dispatch now live in InteractScreen (chat.rs):
- Enter pushes directly to SharedMindState.input (no app.submitted hop)
- sync_from_agent displays pending input with dimmed color
- Slash command table moved from event_loop.rs to chat.rs
- cmd_switch_model kept as pub fn for tool-initiated switches

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/tools/control.rs

@@ -14,7 +14,7 @@ pub(super) fn tools() -> [super::Tool; 3] {
                        .ok_or_else(|| anyhow::anyhow!("'model' parameter is required"))?;
                    if model.is_empty() { anyhow::bail!("'model' parameter cannot be empty"); }
                    if let Some(agent) = agent {
-                       let mut a = agent.lock().unwrap();
+                       let mut a = agent.lock().await;
                        a.pending_model_switch = Some(model.to_string());
                    }
                    Ok(format!("Switching to model '{}' after this turn.", model))
@@ -24,7 +24,7 @@ pub(super) fn tools() -> [super::Tool; 3] {
                parameters_json: r#"{"type":"object","properties":{}}"#,
                handler: |agent, _v| Box::pin(async move {
                    if let Some(agent) = agent {
-                       let mut a = agent.lock().unwrap();
+                       let mut a = agent.lock().await;
                        a.pending_yield = true;
                        a.pending_dmn_pause = true;
                    }
@@ -36,7 +36,7 @@ pub(super) fn tools() -> [super::Tool; 3] {
                handler: |agent, v| Box::pin(async move {
                    let msg = v.get("message").and_then(|v| v.as_str()).unwrap_or("Waiting for input.");
                    if let Some(agent) = agent {
-                       let mut a = agent.lock().unwrap();
+                       let mut a = agent.lock().await;
                        a.pending_yield = true;
                    }
                    Ok(format!("Yielding. {}", msg))

src/agent/tools/mod.rs

@@ -29,7 +29,7 @@ fn default_timeout() -> u64 { 120 }
 /// Async tool handler function.
 /// Agent is None when called from contexts without an agent (MCP server, subconscious).
 pub type ToolHandler = fn(
-    Option<std::sync::Arc<std::sync::Mutex<super::Agent>>>,
+    Option<std::sync::Arc<tokio::sync::Mutex<super::Agent>>>,
     serde_json::Value,
 ) -> Pin<Box<dyn Future<Output = anyhow::Result<String>> + Send>>;
 
@@ -94,11 +94,11 @@ pub async fn dispatch(
 pub async fn dispatch_with_agent(
     name: &str,
     args: &serde_json::Value,
-    agent: Option<std::sync::Arc<std::sync::Mutex<super::Agent>>>,
+    agent: Option<std::sync::Arc<tokio::sync::Mutex<super::Agent>>>,
 ) -> String {
     // Look up in agent's tools if available, otherwise global
     let tool = if let Some(ref a) = agent {
-        let guard = a.lock().unwrap();
+        let guard = a.lock().await;
         guard.tools.iter().find(|t| t.name == name).copied()
     } else {
         None

src/agent/tools/working_stack.rs

@@ -20,7 +20,7 @@ pub fn tool() -> super::Tool {
         parameters_json: r#"{"type":"object","properties":{"action":{"type":"string","enum":["push","pop","update","switch"],"description":"Stack operation"},"content":{"type":"string","description":"Task description (for push/update)"},"index":{"type":"integer","description":"Stack index (for switch, 0=bottom)"}},"required":["action"]}"#,
         handler: |agent, v| Box::pin(async move {
             if let Some(agent) = agent {
-                let mut a = agent.lock().unwrap();
+                let mut a = agent.lock().await;
                 Ok(handle(&v, &mut a.context.working_stack))
             } else {
                 anyhow::bail!("working_stack requires agent context")