feat: add doctor command for diagnosing installs and cleaning stale daemon state (#1254)

* feat: add `doctor` command for install diagnostics and cleanup

Adds `agent-browser doctor`, a one-shot diagnostic that checks
environment, Chrome install, daemon state, config, encryption key,
providers, network reachability, and a live headless launch test.
Auto-cleans stale `.sock` / `.pid` / `.version` / `.stream` sidecar
files on every run. Destructive repairs (reinstall Chrome, purge old
state, close version-mismatched daemons, generate missing encryption
key) are gated behind `--fix`. Supports `--offline`, `--quick`, and
`--json`.

* fixes

cli/src/native/state.rs

@@ -714,14 +714,21 @@ pub fn dispatch_state_command(cmd: &Value) -> Option<Result<Value, String>> {
     }
 }
 
-pub fn get_sessions_dir() -> PathBuf {
+/// Return the agent-browser state root (`~/.agent-browser`, falling back to
+/// `<tempdir>/agent-browser` when the home directory can't be resolved).
+/// This is the parent of `sessions/`, auth storage, and the encryption key.
+pub fn get_state_dir() -> PathBuf {
     if let Some(home) = dirs::home_dir() {
-        home.join(".agent-browser").join("sessions")
+        home.join(".agent-browser")
     } else {
-        std::env::temp_dir().join("agent-browser").join("sessions")
+        std::env::temp_dir().join("agent-browser")
     }
 }
 
+pub fn get_sessions_dir() -> PathBuf {
+    get_state_dir().join("sessions")
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;