Add daemon startup smoke test and let it run on a PC in debug_mode

v0.11.0 shipped a daemon binary that built fine but didn't actually serve
a working frontend. CI was green. Nothing in the pipeline asserted that
the built binary comes up and serves something.

Add daemon/tests/smoke.rs as an integration test that spawns the built
binary against a tempdir-backed config with debug_mode = true, picks an
ephemeral port, and asserts:

- GET /index.html is 2xx and the decompressed body contains "Rayhunter"
- GET /api/qmdl-manifest is 2xx
- the daemon exits cleanly on SIGINT

Captures the daemon's stderr into a buffer so startup/shutdown failures
print actionable context instead of just "did not start listening".

Runs as part of the regular cargo test invocation, no new CI job.

For the smoke test (and #826) to work, the daemon needs to come up on a
PC without /dev/diag, a screen, or wpa_supplicant. The DIAG read thread,
display driver, and key input were already gated on debug_mode. Gate the
two remaining device-dependent workers the same way:

- run_battery_notification_worker (polls battery sysfs paths)
- wifi_station::run_wifi_client (talks to wpa_supplicant)

doc/installing-from-source.md gains a "Running the daemon on your PC"
section. doc/porting.md drops its duplicate debug_mode line and links to
the new section.

Closes #826.

daemon/src/main.rs

@@ -277,12 +277,14 @@ async fn run_with_config(
         analysis_tx.clone(),
     );
 
-    run_battery_notification_worker(
-        &task_tracker,
-        config.device.clone(),
-        notification_service.new_handler(),
-        shutdown_token.clone(),
-    );
+    if !config.debug_mode {
+        run_battery_notification_worker(
+            &task_tracker,
+            config.device.clone(),
+            notification_service.new_handler(),
+            shutdown_token.clone(),
+        );
+    }
 
     run_notification_worker(
         &task_tracker,
@@ -291,12 +293,14 @@ async fn run_with_config(
     );
 
     let wifi_status = Arc::new(RwLock::new(WifiStatus::default()));
-    wifi_station::run_wifi_client(
-        &task_tracker,
-        &config.wifi_config(),
-        shutdown_token.clone(),
-        wifi_status.clone(),
-    );
+    if !config.debug_mode {
+        wifi_station::run_wifi_client(
+            &task_tracker,
+            &config.wifi_config(),
+            shutdown_token.clone(),
+            wifi_status.clone(),
+        );
+    }
 
     if !config.webdav.url.trim().is_empty() {
         run_webdav_upload_worker(