Per-peer pan + EQ ("Pan and EQ" tab) — off by default, held for next release

New feature (Ed's jam-mixing request): pan and EQ each peer's signal independently.

Engine (zero added latency — per-sample, applied to each peer's isolated block just
before the mix): PeerDspChain (balance pan + RBJ biquad EQ) built on the UI thread and
swapped onto SessionPlayout via a volatile reference; PlayoutEngine remembers it per
address so a reconnecting peer keeps its shaping; AudioReceiver.SetPeerDsp facade.

Model: per-profile PeerShaping dict (keyed by peer address) + EnablePan/EnableEqForPeers
master switches; machine-wide AppConfig.ShowPanEqTab. Fixed band layouts in PeerEqBands
(3-band tone control: bass/mids/treble shelves+bell; 10-band ISO graphic EQ), +/-12 dB.

UI: a "Pan and EQ" tab (before Audio profile, shown only when ShowPanEqTab is on) with
the two enables, a connected-peer picker, a pan slider (balance, keeps stereo), a
"reset EQ" button (clears both modes' bands, leaves pan), a 3/10-band mode picker and its
band sliders — all TrackBars (arrow + page-up/down), updating in real time and saved per
profile. Sliders set a friendly AccessibleName on change (pan centre/left/right %, band
dB). "Show the Pan and EQ tab" checkbox added to Preferences > General.

Everything is off by default (tab hidden, both enables off), so this is dormant for all
users until switched on. Builds clean. Pending Ed's hands-on testing before release.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.Core/AppConfig.cs

@@ -68,6 +68,12 @@ public sealed class AppConfig
     /// already running quietly". Default false.</summary>
     public bool StartMinimised { get; set; }
 
+    /// <summary>If true, the main window shows a "Pan and EQ" tab (positioned before "Audio profile")
+    /// for setting per-peer panning and EQ. Off by default; toggled by "Show pan and EQ tab" on the
+    /// Preferences General tab. Machine-wide (a UI-visibility preference, like which tabs exist) — the
+    /// pan/EQ VALUES are saved per profile, in <see cref="Profile.PeerShaping"/>.</summary>
+    public bool ShowPanEqTab { get; set; }
+
     /// <summary>If true (the default), RemSound plays the startup cue once, right after this
     /// copy wins the single-instance takeover and before the profile loads. Machine-wide (not
     /// per-<see cref="Profile"/>) because it fires before any profile — and its per-profile