Fix auto-lookback trigger and add version tracking (#20)

* Fix auto-lookback trigger and add version tracking

- Trigger on stdin inactivity instead of render time
- Only dump when new output exists since last dump
- Default timeout 5s -> 15s
- Embed git hash in version output
- Document macOS config path

crates/claude-chill/build.rs

@@ -0,0 +1,38 @@
+use std::process::Command;
+
+fn main() {
+    println!("cargo:rerun-if-changed=.git/HEAD");
+    println!("cargo:rerun-if-changed=.git/index");
+
+    let git_hash = get_git_hash();
+    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
+}
+
+fn get_git_hash() -> String {
+    let hash = match Command::new("git")
+        .args(["rev-parse", "--short", "HEAD"])
+        .output()
+    {
+        Ok(output) if output.status.success() => String::from_utf8(output.stdout)
+            .ok()
+            .map(|s| s.trim().to_string()),
+        _ => None,
+    };
+
+    let Some(hash) = hash else {
+        return "git not found during build, version unavailable".to_string();
+    };
+
+    let is_dirty = Command::new("git")
+        .args(["status", "--porcelain"])
+        .output()
+        .ok()
+        .map(|output| !output.stdout.is_empty())
+        .unwrap_or(false);
+
+    if is_dirty {
+        format!("{}-dirty", hash)
+    } else {
+        hash
+    }
+}