fix(ui): FA5 -- repair two NUL bytes corrupted into BlankSentinel's literal spaces

A tool-layer artifact from the original FA5 commit (7ed79eaf) silently
replaced the leading and trailing ASCII space (0x20) in
`BlankSentinel = " blank "` with NUL (0x00) bytes -- verified byte-for-
byte via PowerShell (two NUL bytes total in the whole file, both
adjacent to the literal's "blank" text). C# tolerates an embedded NUL in
a string literal (it compiles and runs fine, since the constant is only
ever used as an internal dedup sentinel, never rendered), so this never
surfaced as a build or test failure -- caught only by an incidental
`file`/`grep -a` binary-content check while re-reviewing the finished
slice. Replaced the two NUL bytes with the intended spaces at the exact
byte offsets; swept every other file this slice touched (Runtime/App/
tests/docs) for the same corruption and found none.

No behavior change: full solution suite still 13,296 passed / 4 skipped
/ 0 failed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/UI/Layout/SocialAllegiancePageController.cs

@@ -154,7 +154,7 @@ public sealed class SocialAllegiancePageController
     /// <see cref="Tick"/> a false "unchanged" no-op, leaving the widget at
     /// its import-time (non-blank) text instead of retail's literal single
     /// space.</summary>
-    private const string BlankSentinel = "blank";
+    private const string BlankSentinel = " blank ";
 
     /// <summary>The live read/write seam this page binds to — mirrors
     /// <see cref="SocialFellowshipPageController.Bindings"/>'s shape.