refactor(log): in-place writer lifecycle and span-based core observability (#7889)

* refactor(log): migrate logging to tracing-estuary pipeline

Swap flexi_logger + clash-verge-logger wiring for the tracing-estuary
crate: buffered file sink with explicit panic/exit drains, live level
switching, and tokio-trace/chrome-trace behind crate features.

AsyncLogger moves in-house (VecDeque ring); file format and rotation
stay unchanged.

* fix(log): reset sidecar writer in place and re-pin service-ipc v2.6.7

Rebuilding the sidecar FileLogWriter on config changes leaked flexi's
unstoppable flusher thread plus an fd each time; the writer is now flushed
and reset in place, matching what the service crate does.
get_clash_logs_by_service drops the CompactString conversion layer now that
service-ipc v2.6.7 returns plain Vec<String>, and AsyncLogger is renamed
LogRing to match.

* refactor(log): span-based observability and log noise cleanup

Instrument spans carry the structure flat lines never could: the core-start
spine (mode, readiness/owner generations, pid, config file), proxy apply and
clear routes with guard generations, service IPC sessions with refusal codes
and outcomes, profile-switch terminal outcomes, subscription fetch strategies,
core upgrades with per-proxy version probes, backup flows, timer tasks, config
generation uids, and the startup setup flow; running-mode changes emit one
guarded transition event each.
~90 hand-written noise lines are gone or demoted (entry+success pairs, polled
getter echoes, phase brackets, window sub-steps, platform install chatter);
errors keep their anyhow chain, operation name, and item id, and swallowed
retry results surface per attempt.

src-tauri/src/core/network_watch.rs

@@ -43,6 +43,11 @@ pub fn start() {
     };
     CFRunLoop::get_main().add_source(&source, unsafe { kCFRunLoopCommonModes });
     ARMED.store(true, Ordering::Release);
+    logging!(
+        debug,
+        Type::Core,
+        "network watch armed; the system proxy is re-applied on network changes"
+    );
 }
 
 fn on_change(_: SCDynamicStore, _: CFArray<CFString>, (): &mut ()) {