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/AppConfig.cs

@@ -50,12 +50,18 @@ public sealed class AppConfig
     public bool SaveProfileConfirmationSuppressed { get; set; }
 
     /// <summary>True if the user has ticked "do not show me this message again" on the
-    /// "this profile is read-only, save was skipped" popup. Once ticked, Ctrl+S / File → Save
-    /// on a read-only profile silently does nothing instead of explaining why — the user
-    /// has acknowledged that they know it's a no-op. Machine-local (not per-profile) so the
-    /// preference sticks across profile switches; the prompt itself is the same wording on
-    /// any read-only profile so a single dismissal applies everywhere. 2026-05-22.</summary>
-    public bool SaveOnReadOnlyMessageSuppressed { get; set; }
+    /// "you are saving onto a read-only profile" warning. Once ticked, Ctrl+S / File → Save
+    /// on a read-only profile saves silently through the lock instead of warning first.
+    /// Machine-local (not per-profile) so the preference sticks across profile switches; the
+    /// prompt itself is the same wording on any read-only profile so a single dismissal
+    /// applies everywhere. 2026-05-23 — semantic shift from v2.x: in v2.x the read-only lock
+    /// hard-blocked explicit saves and this flag suppressed the explanatory "save was skipped"
+    /// popup. In v3.0 the lock only suppresses the automatic "you have unsaved changes" prompt
+    /// on close / profile switch; explicit Ctrl+S / File → Save now goes through with a
+    /// one-time warning gated by this flag. The JSON key was renamed alongside the semantic
+    /// change so users upgrading from v2.x see the new warning at least once — a v2.x
+    /// suppression flag is no longer applicable and is silently discarded on load.</summary>
+    public bool SaveOnReadOnlyWarningSuppressed { get; set; }
 
     /// <summary>If true, RemSound minimises to the system tray immediately after the main
     /// window finishes loading. Lets the user "boot up the machine and have RemSound