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/Cargo.toml

@@ -47,3 +47,7 @@ rustls-post-quantum = { version = "0.2.4", optional = true }
 async-trait = "0.1.88"
 utoipa = { version = "5.4.0", optional = true }
 url = "2.5.4"
+
+[dev-dependencies]
+reqwest = { version = "0.12.20", default-features = false, features = ["gzip"] }
+tempfile = "3.10.2"