Bump to v3.0.0: Opus live latency, codec rename, profile-resume after update, save-through-lock

* New "Opus, live latency" codec mode: 2.5 ms frames (120 samples/ch at 48 kHz)
  via the float-input encode path. End-to-end codec delay drops to ~5 ms (vs
  ~12.5 ms at standard 10 ms Opus). Test on LAN: 400 pps/lane, zero missed /
  reordered / duplicate packets, ~15 ms one-way saved end-to-end.

* Wire-format change: AudioFormatInfo.FrameDurationMilliseconds renamed to
  FrameSamplesPerChannel (int sample-count at announced sample rate). Removes
  the lossy 48000*ms/1000 conversion that couldn't represent 2.5 ms. v3 <-> v3
  exact; v3 <-> v2 still passes audio (Opus decoder is self-describing from
  packet TOC) but v2 side over-sizes its buffer wildly. v2.x profiles auto-
  migrate via <120 sentinel rule in RemSoundSettingsStore (anything below 120
  is treated as legacy ms and multiplied by 48). Profile JSON key kept as
  OpusFrameMilliseconds via [JsonPropertyName] so old profile files still load.

* Codec dropdown rebuilt with use-case names: "PCM 48K 24 bit - uncompressed",
  "Opus, broadcast quality - loss tolerant", "Opus, live latency - for jamming
  and monitoring". Middle 10 ms option retired; saved 480-sample profiles
  collapse to broadcast quality (safer-side default).

* Profile auto-resume after self-update: RemSoundUpdater writes a one-shot
  _resume-after-update.txt sentinel containing the active profile title before
  exit; Program.Main reads + deletes it on next start and silently loads that
  profile, skipping the picker. Helper batch's robocopy /XF excludes the
  sentinel and the failure-branch cleans it up if the install aborts. Falls
  through to normal startup behaviour (StartWithProfileTitle or picker) if the
  sentinel is missing, empty, or names a profile that no longer exists.

* Read-only profile saves now go through on explicit Ctrl+S / File -> Save
  with a one-time TaskDialog warning ("Save anyway" / "Cancel" + Do-not-show-
  again). Lock continues to suppress the automatic unsaved-changes prompt on
  close / profile switch (its main job). AppConfig.SaveOnReadOnlyMessageSuppressed
  renamed to SaveOnReadOnlyWarningSuppressed; v2.x suppression flag is silently
  discarded since the behaviour changed and the user needs to see the warning
  once on each machine.

* Manual (readme.html) updated: codec table rewritten with the three new
  choices and corrected bandwidth figures, send-rate description updated, new
  sections "The same profile picks up automatically after an update" and
  "Saving on purpose while a profile is locked".

* Subsumes the never-separately-released v2.2 work: native Opus encoder
  (~97% less per-second memory churn on Opus send path via Concentus.Native),
  efficiency tidy-ups (item 4 ASIO probe rate, item 6 WaitHandle, item 7
  snapshot cache, items 14/16 heartbeat + discovery), legacy cleanup
  (items 30/34/35/36: KeepAlive infrastructure, drift drop/repeat/accumulator
  fields, fan-out cache stat). New diagnostic columns cpu/memMB/wsMB/
  allocKBps/captureMs/sendMs/recvMs/renderMs gated on Enable-logs.

About dialog updated with v3.0 block at top; v2.2 block retained for the
subsumed work.

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

src/RemSound.Core/Profile.cs

@@ -62,7 +62,17 @@ public sealed class Profile
     // === Connectivity & transport ===
     public int AudioPort { get; set; } = 47830;
     public int CodecRaw { get; set; } = (int)AudioTransportCodec.Pcm;
-    public int OpusFrameMilliseconds { get; set; } = 10;
+    /// <summary>Opus frame size in samples-per-channel at 48 kHz. 120 = 2.5 ms, 240 = 5 ms,
+    /// 480 = 10 ms (default), 960 = 20 ms. Renamed from <c>OpusFrameMilliseconds</c> in the
+    /// v3.0 wire-format refactor (2026-05-23). The JSON key is kept as
+    /// <c>OpusFrameMilliseconds</c> for back-compat with v2.x profile files; on read,
+    /// <see cref="RemSoundSettingsStore.LoadOpusFrameSamplesPerChannel"/> disambiguates the
+    /// legacy integer-ms encoding (5/10/20) from the new sample-count encoding
+    /// (120/240/480/960) using a sentinel: any persisted value &lt; 120 is treated as ms and
+    /// multiplied by 48. v2.x readers loading a v3.x profile see e.g. 480 and clamp it to
+    /// their accept-list (which only knows 10 or 20), defaulting silently to 10 ms.</summary>
+    [JsonPropertyName("OpusFrameMilliseconds")]
+    public int OpusFrameSamplesPerChannel { get; set; } = 480;
     public int SendRateRaw { get; set; } = (int)SendRate.Standard;
     public bool TightLatencyMode { get; set; }
     /// <summary>True if this profile asks Windows to keep the RemSound process in