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/styles/components/modal.css

@@ -138,6 +138,133 @@
   padding-right: 2px;
 }
 
+/* Logs tab manages its own internal scroll: the body becomes a flex column with
+   hidden overflow so only the log view scrolls, not the controls/filter. */
+.sidebar-perf-modal__body--logs {
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+  padding-right: 0;
+}
+
+.perf-logs {
+  display: flex;
+  flex-direction: column;
+  flex: 1 1 auto;
+  min-height: 0;
+  gap: 8px;
+}
+
+.perf-logs__controls {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: flex-end;
+  gap: 8px;
+  flex: 0 0 auto;
+}
+
+.perf-logs__control {
+  display: flex;
+  flex-direction: column;
+  gap: 3px;
+}
+
+.perf-logs__control-label {
+  font-size: 11px;
+  color: var(--text-muted);
+}
+
+.perf-logs__btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  padding: 5px 10px;
+  font-size: 12px;
+  border-radius: 7px;
+  border: 1px solid color-mix(in srgb, var(--text-muted) 30%, transparent);
+  background: transparent;
+  color: var(--text-primary);
+  cursor: pointer;
+}
+
+.perf-logs__btn:hover {
+  background: color-mix(in srgb, var(--text-muted) 16%, transparent);
+}
+
+.perf-logs__btn[aria-pressed='true'] {
+  border-color: color-mix(in srgb, var(--accent) 55%, transparent);
+  color: var(--accent);
+}
+
+.perf-logs__filter {
+  width: 100%;
+  flex: 0 0 auto;
+  padding: 6px 9px;
+  font-size: 12px;
+  border-radius: 7px;
+  border: 1px solid color-mix(in srgb, var(--text-muted) 28%, transparent);
+  background: var(--bg-secondary, rgba(0, 0, 0, 0.2));
+  color: var(--text-primary);
+}
+
+.perf-logs__view {
+  position: relative;
+  flex: 1 1 auto;
+  min-height: 0;
+  overflow-y: auto;
+  padding: 8px 10px;
+  border-radius: 8px;
+  background: color-mix(in srgb, var(--text-muted) 8%, transparent);
+  border: 1px solid color-mix(in srgb, var(--text-muted) 18%, transparent);
+  font-family: var(--font-mono, ui-monospace, SFMono-Regular, Menlo, monospace);
+  font-size: 11.5px;
+  line-height: 1.5;
+}
+
+.perf-logs__line {
+  white-space: pre-wrap;
+  word-break: break-word;
+  color: var(--text-primary);
+}
+
+.perf-logs__line--marker {
+  color: var(--accent);
+  opacity: 0.8;
+  text-align: center;
+  padding: 2px 0;
+}
+
+.perf-logs__empty {
+  color: var(--text-muted);
+  font-size: 12px;
+  padding: 1.5rem 0.5rem;
+  text-align: center;
+}
+
+.perf-logs__status {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 10px;
+  flex: 0 0 auto;
+  font-size: 11px;
+  color: var(--text-muted);
+}
+
+.perf-logs__jump {
+  padding: 3px 9px;
+  font-size: 11px;
+  border-radius: 6px;
+  border: 1px solid color-mix(in srgb, var(--accent) 45%, transparent);
+  background: transparent;
+  color: var(--accent);
+  cursor: pointer;
+}
+
+.perf-logs__jump:hover {
+  background: color-mix(in srgb, var(--accent) 14%, transparent);
+}
+
 .perf-monitor-empty {
   display: flex;
   flex-direction: column;