Covers the matrix from the issue: disabled hot-path no-op, window
aggregation count/p95, window-reset isolation, the full stall-threshold
matrix (panUpdate/waterfallUpdate/render/frameAge/udpDrain/input),
drag-aware UI lag thresholds, frame-restart counter, percentile-95
boundary cases (empty, single, 100-sorted, 100-reversed), and window
timing across the 1s boundary.

Adds two test seams on PerfTelemetry — `setClockOverrideForTest(qint64)`
to pin nowNs() to a synthetic value, and `resetForTest()` to zero
aggregation state between cases. The clock override is a single relaxed
atomic load in the hot path; when zero (production default) the original
steady_clock path is used unchanged.

The test file declares its own Q_LOGGING_CATEGORY for `aether.perf`
rather than linking LogManager, which would otherwise pull in
AppSettings/AsyncLogWriter. Output is captured via qInstallMessageHandler
and matched on key=value field extraction from the emitted PerfStall /
PerfSummary lines.

Blast radius: risk_score=0.435, 19 high-risk affected (top:
AetherSDR::MainWindow::MainWindow, MainWindow::wirePanadapter,
MainWindow::buildMenuBar). All callers reach PerfTelemetry through
its existing public record* API which is unchanged in shape or
behavior; the additions are two new public test-only methods plus
one relaxed atomic load in nowNs().

Covers the matrix from the issue: disabled hot-path no-op, window
aggregation count/p95, window-reset isolation, the full stall-threshold
matrix (panUpdate / waterfallUpdate / render / frameAge / udpDrain /
input), drag-aware UI lag thresholds (50 ms idle / 33 ms drag), the
frame-restart counter, percentile-95 boundary cases (empty / single /
[1..100] sorted / 100 reversed), and the 1 s window cadence (no fire
at 950 ms, fire at 1100 ms).

Two purely additive test seams land on PerfTelemetry:
`setClockOverrideForTest(qint64)` pins nowNs() to a synthetic value so
window timing is deterministic without real sleeps, and `resetForTest()`
zeroes aggregation state between cases so the singleton doesn't leak
between tests. The clock override is a single relaxed atomic load in
the hot path; when zero (production default) the original steady_clock
path is used unchanged, so the existing record* call surface that the
17 high-risk callers reach is untouched in shape or behavior.

The test executable links LogManager.cpp + AsyncLogWriter.cpp +
AppSettings.cpp instead of redeclaring its own Q_LOGGING_CATEGORY for
`aether.perf` — this honors Principle III's consolidation (one
canonical definition site per category, per #2770) and matches the
linkage pattern established by `ax25_libmodem_shim_test`. Output is
captured via qInstallMessageHandler filtered to `aether.perf` and
matched on key=value field extraction from emitted PerfStall and
PerfSummary lines.

Blast radius: risk_score=0.418, 17 high-risk affected (top:
MainWindow::MainWindow, MainWindow::wirePanadapter, MainWindow::buildUI,
RadioModel::onStatusReceived, MainWindow::buildMenuBar). All these
reach PerfTelemetry through its existing public record* API which is
unchanged; the additions are two new public test-only methods plus one
relaxed atomic load in nowNs() that is a no-op when the override is
the default zero.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>