feat(windows/client): logs persist — %LOCALAPPDATA%\punktfunk\logs\client.log

The shell is a windows_subsystem binary and spawns punktfunk-session with
CREATE_NO_WINDOW + inherited stderr: a normal GUI/MSIX launch has no
console, so every log line — the shell's and the session's whole
receive/decode/present forensic trail — evaporated exactly when a user
hit something worth reporting. The 2026-07 PyroWave latency-sawtooth
report had to be triaged from host logs alone; the deciding evidence
(clock re-sync vs backlog-flush lines) lives client-side.

- New logfile module: %LOCALAPPDATA%\punktfunk\logs\client.log,
  the host's rotation convention (10 MB cap -> .old at next start, one
  generation), best-effort (no dir -> plain stderr, never a startup
  failure).
- The tracing subscriber tees to stderr AND the file (ANSI off — the
  file is what users send); startup logs the path.
- The spawned session's stderr is piped through the same tee,
  line-buffered — dev-terminal runs keep their interleaved output,
  GUI runs finally keep anything at all.
- The --console path and the punktfunk-console.exe MSIX shim forward
  the same way (a couch launch has no console either).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/windows/src/bin/punktfunk-console.rs

@@ -13,8 +13,17 @@
 // console behind the couch UI looks like a crash.
 #![cfg_attr(windows, windows_subsystem = "windows")]
 
+// The shared client log sink (std-only): a couch launch has no console, so the session's
+// stderr would otherwise evaporate — same reasoning as the shell's tee. This shim only
+// initializes + forwards; the module's subscriber-side surface stays unused here.
+#[cfg(windows)]
+#[path = "../logfile.rs"]
+#[allow(dead_code)]
+mod logfile;
+
 #[cfg(windows)]
 fn main() {
+    logfile::init();
     // The session binary ships beside us in the package; fall back to PATH for a dev run.
     let session = std::env::current_exe()
         .ok()
@@ -27,7 +36,14 @@ fn main() {
     if !std::env::args().any(|a| a == "--windowed") {
         cmd.arg("--fullscreen");
     }
-    match cmd.status() {
+    cmd.stderr(std::process::Stdio::piped());
+    let run = cmd.spawn().and_then(|mut child| {
+        if let Some(stderr) = child.stderr.take() {
+            logfile::forward_child_stderr(stderr);
+        }
+        child.wait()
+    });
+    match run {
         Ok(st) => std::process::exit(st.code().unwrap_or(0)),
         Err(_) => std::process::exit(1),
     }