Summary

Consolidates client-side DSP from three surfaces (VFO DSP grid,
spectrum overlay sub-panel, AetherDSP dialog) down to one: a new
docked Aetherial Noise Reduction applet on the PooDoo RX side,
which the Settings-menu dialog also embeds via shared
`AetherDspWidget`. Radio-side DSP now lives only on `VfoWidget`.

Changes

• New `AetherDspWidget` — extracts the dialog body into a
  reusable widget with compact-mode support; both `AetherDspDialog`
  and the new `ClientRxDspApplet` embed it. Single source of truth
  for AppSettings persistence.
• New `ClientRxDspApplet` — 250 px-wide docked tile with
  exclusive DSP selector (NR2 / NR4 / MNR / DFNR / RN2 / BNR) +
  per-DSP control pages in a stacked widget. Single-click on the RX
  chain DSP tile bypasses; double-click opens the full editor.
• VFO DSP grid — drops the six client-side buttons; gains a
  shared DSP-level slider with a push/pop activation stack so the
  slider tracks the most-recently-enabled radio DSP and hides
  cleanly when no slider-bearing DSP is active.
• Spectrum overlay menu — DSP sub-panel removed entirely.
  Drops 11 toggle/right-click signals, six button accessors, the
  15-row `DspRow` grid, and the build/sync/toggle triplet.
• TX chain applets — visibility now decoupled from bypass
  state; bypassed applets dim instead of disappearing (matches
  Aetherial TX EQ).
• NR2 enable path — wisdom generation now runs through
  `MainWindow::enableNr2WithWisdom()` for both the applet and the
  RX chain widget, fixing the NR4→NR2 transition crash caused by
  FFTW wisdom version mismatch (Avoid NR2 wisdom generation on audio thread #2275).
• NR4 polish — MMSE label, info paragraph at 12 px across all
  panels, undo/reset icon repositioning, padding fixes.
• Platform guards — MNR dimmed/disabled on non-macOS, BNR
  guarded by `HAVE_BNR`.

Test plan

• Launch app — initial visibility shows only enabled chain
  applets, no double-display of TX+RX
• RX chain: single-click `[DSP]` tile bypasses; click again
  re-enables the last-selected DSP
• RX chain: double-click `[DSP]` opens the full
  `AetherDspDialog`
• Aetherial Noise Reduction applet: exclusive selector
  switches the engine DSP and the visible parameter page
• VFO DSP grid: shared level slider appears for slider-bearing
  DSPs, hides when last one disabled, falls back to next active
  DSP if multiple are enabled
• Spectrum overlay menu opens cleanly with no DSP entry
• NR4 → NR2 transition does not crash (PR Avoid NR2 wisdom generation on audio thread #2275 wisdom path)
• Opus / SmartLink active → NR2 button disabled in applet
• Settings → AetherDSP dialog still works (shares widget with
  applet)

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