feat(perf): live runtime logs tab in Performance Probe (#946)

* feat(perf): live runtime logs tab in Performance Probe

Add a Logs tab that streams the backend runtime log ring buffer in-app, so the
stdout/stderr console (unreachable on Windows without exporting) can be read
live. The buffer now tracks a monotonic seq; a new tail_runtime_logs command
returns lines incrementally and get_logging_mode reports the current depth.

The tab has a depth switch (off/normal/debug) mirroring app settings, a line cap
(500-5000), pause/clear, auto-follow, and an ordered comma-separated word filter
where a plain word includes and a -word excludes, applied left to right as
layers (sequence matters).

* docs(changelog): note Performance Probe logs tab (PR #946)

Add CHANGELOG entry and credits line for the live runtime logs tab.

* fix(perf): pin log view position when scrolled up

Auto-scroll keeps the logs tab at the tail, but once the user scrolls up the
view now stays put — the previously-topmost line is re-pinned each tick while
the log keeps appending below for further scrolling. History under the viewport
is no longer trimmed while scrolled up (kept up to the ring-buffer ceiling); the
cap is re-applied when following resumes. Buffer overflow is shown in the status
line instead of an injected marker row.

* fix(perf): scope logs tab to its own internal scroll

The whole probe body scrolled (controls + filter + log) because the log
container sized via height:100%, which WebKitGTK does not resolve against the
flex body. Make the body a flex column with hidden overflow on the Logs tab and
let the log view flex-fill, so depth/keep/pause/clear and the filter stay fixed
while only the log lines scroll.

src-tauri/src/lib.rs

@@ -612,6 +612,8 @@ pub fn run() {
             linux_wayland_text_render_settings_available,
             set_linux_wayland_text_render_profile,
             set_logging_mode,
+            get_logging_mode,
+            tail_runtime_logs,
             export_runtime_logs,
             frontend_debug_log,
             performance_cpu_snapshot,