delete ProcessTracker — replaced by ActiveToolCall + KillOnDrop

All process management now goes through active_tools:
- TUI reads metadata (name, elapsed time)
- Ctrl+K aborts handles (KillOnDrop sends SIGTERM)
- Running count from active_tools.len()

No more separate PID tracking, register/unregister, or
ProcessInfo. One data structure for everything.

Co-Developed-By: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

src/agent/tools/bash.rs

@@ -12,7 +12,7 @@ use serde_json::json;
 use std::process::Stdio;
 use tokio::io::AsyncReadExt;
 
-use super::{ToolDef, ProcessTracker, default_timeout};
+use super::{ToolDef, default_timeout};
 
 /// RAII guard that SIGTERMs the process group on drop.
 /// Ensures child processes are cleaned up when a task is aborted.
@@ -55,7 +55,7 @@ pub fn definition() -> ToolDef {
     )
 }
 
-pub async fn run_bash(args: &serde_json::Value, tracker: &ProcessTracker) -> Result<String> {
+pub async fn run_bash(args: &serde_json::Value) -> Result<String> {
     let a: Args = serde_json::from_value(args.clone())
         .context("invalid bash arguments")?;
     let command = &a.command;
@@ -73,7 +73,6 @@ pub async fn run_bash(args: &serde_json::Value, tracker: &ProcessTracker) -> Res
 
     let pid = child.id().unwrap_or(0);
     let kill_guard = KillOnDrop(pid);
-    tracker.register(pid, command).await;
 
     // Take ownership of stdout/stderr handles before waiting,
     // so we can still kill the child on timeout.
@@ -139,14 +138,12 @@ pub async fn run_bash(args: &serde_json::Value, tracker: &ProcessTracker) -> Res
             Err(anyhow::anyhow!("Command failed: {}", e))
         }
         Err(_) => {
-            // Timeout — kill the process group
-            tracker.kill(pid).await;
+            // Timeout — KillOnDrop will SIGTERM the process group
             Err(anyhow::anyhow!("Command timed out after {}s: {}", timeout_secs, command))
         }
     };
 
     // Process completed normally — defuse the kill guard
     std::mem::forget(kill_guard);
-    tracker.unregister(pid).await;
     result
 }