Volume/pan/EQ tab overhaul: one master switch, peer checklist, 16-band parametric EQ

Reworks the per-peer shaping tab (held for next release):

 * Renamed the tab to "Volume, pan and EQ for peers"; the Preferences toggle now defaults ON.
 * Collapsed the two master switches (Enable EQ / Enable pan) into ONE: "Enable volume, pan and
   EQ for all peers" (Alt+E). Volume now obeys it too. PeerDspChain.Build takes a single enabled
   flag; Profile.EnableAllPeerShaping replaces the two bools (old ones kept for load-migration).
 * Peer picker is now a CheckedListBox: ticking a peer shapes them (per-peer bypass via new
   PeerShaping.Enabled, default true); the focused row is the one the controls edit. Effective
   shaping = master switch AND that peer's tick. Letter-nav suppressed so keys never toggle a tick.
 * Three EQ modes, renamed: "3 band simple EQ", "12 band advanced graphic EQ", and the new
   "16 band parametric EQ" (PeerEqMode.Parametric16Band).
 * Parametric EQ: up to 16 user bands, each a boost/cut across a start->end range (PeerShaping
   .ParametricBands; ParametricToPeaking maps range -> peaking centre+Q, shared by DSP and curve).
   Add band dialog (spin-or-type, numeric-only, live preview, OK/Escape); Bands list sorted
   bass->treble reading "X Hz to Y Hz, plus/minus N dB"; Delete key / Delete button, multi-select.
   Set peer EQ to default clears the parametric list too.
 * dB now spoken as words ("plus 3 dB" / "minus 6 dB" / "flat") on the graphic sliders and the
   parametric list, since NVDA users typically have punctuation off and never hear a "+".
 * New unbound machine-wide global shortcut "Toggle volume, pan and EQ for all peers" (not stored
   in any profile) via the hotkey controller + settings store.
 * Renamed the Inputs/outputs "Set volume for all received audio" to "Master receive volume".
 * Added EqCurveControl: a purely-visual EQ response graph (not focusable, invisible to NVDA).
 * Full manual sweep (readme.html + regenerated MANUAL.md).

Build clean; --selftest passes. Deployed to both test folders. Held for next release.

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

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