feat(profile): the free budget is pixels and fps, enforced once — with a dev-only release hatch

The paid delta is output quality, so the rule needs to be measurable rather than a word:
921,600 pixels and 30 fps, fail-closed. Models/OutputProfile.cs is that rule as pure
policy — a permitted tier passes through untouched (Pro, or the free tier's own 720p30),
a disallowed one resolves to the best tier the budget allows and carries ITS bitrate, so
a capped user is never offered an 8 Mbps budget for a 720p frame.

Applied once, in BuildEncoderOptions. That is genuinely one place: the stream and the
local recording are two output blocks of ONE ffmpeg process fed by one EncoderOptions,
so there is no second encoder to forget. (commercial.md claimed "both encoders — never
two checks"; the code is stronger than the doc, and the doc is corrected.)

Developer override, as asked: a "Developer mode — all resolutions" checkbox in App
Settings, bound to MainViewModel.DeveloperMode, which feeds HasProOutput. It is not
hidden in a release build — Controls/DeveloperPanel's Page and Compile items are removed
when Configuration != Debug, and OverlayHost adds it at runtime inside #if DEBUG, so a
shipped exe has no BAML for it at all. The setter also refuses the value when
DevBuild.IsDevelopment is false, which is now the single source for that question (the
scoreboard partial had its own duplicate const).

Two traps worth their lines: a `const bool` dev flag makes `if (!Flag) return;` an
unreachable-code warning in one configuration or the other (CS0162), so DevBuild uses
static readonly; and a Condition on an ItemGroup is invisible to a test reading
item.Attribute("Condition") — read the parent.

Tests: 14 pass across OutputProfileTests, AssemblyIdentityTests and StorePackagingTests.
The invariant test is the one that matters: iterate every shipped tier under a free
entitlement and assert none emits more than the budget, so a future 4K tier fails here
instead of shipping to everyone. App builds Debug and Release at 0 warnings.

Helpers/DevBuild.cs

@@ -0,0 +1,29 @@
+namespace ytLive.Helpers;
+
+/// <summary>
+/// Whether this binary is a **development build**.
+///
+/// <para><b>Why <c>static readonly</c> and not <c>const</c>:</b> a const makes
+/// <c>if (!DevBuild.IsDevelopment) return;</c> a compile-time branch, so whichever arm is dead
+/// raises CS0162 — in Debug the guard is dead, in Release the body is. A readonly field is set
+/// once at type init, so both arms compile clean and the JIT folds the branch away.</para>
+///
+/// <para><b>This is not the only defence.</b> The developer panel's XAML and code-behind are
+/// removed from the Release compile entirely (<c>ytLive.csproj</c>, Page/Compile Remove), so a
+/// shipped binary contains no BAML to reveal. This flag is the second lock: it refuses the
+/// value even if something else calls the setter.</para>
+///
+/// <para>Single source for the question. It gates the multi-instance profile
+/// (<see cref="InstanceProfile"/>), the scoreboard's debug seeding, and the all-resolutions
+/// override (<c>MainViewModel.DeveloperMode</c>).</para>
+/// </summary>
+public static class DevBuild
+{
+    /// <summary>True for a Debug compile; false for Release and anything else.</summary>
+    public static readonly bool IsDevelopment =
+#if DEBUG
+        true;
+#else
+        false;
+#endif
+}