fix(ui): fellowship checkbox count, row-text + ListBox Flush doc corrections, promote probe findings to assertions

Mechanism SHOULD-FIX 4: SocialFellowshipPageController's class doc said
0x1000026B holds "all three visible option checkboxes" — the fixture and
the decomp both authors FOUR (Ignore Fellowship Requests / Auto-Accept
Requests / Share XP / Share Loot, 0x10000270-0x10000273). Corrected.

Mechanism SHOULD-FIX 9: SocialPanelRowText.FindDeepest's doc promised
"the deepest UiText descendant" but the implementation returns the LAST
match in pre-order traversal order, which only equals the deepest when
the subtree is a single chain. Both real row templates ARE single
chains today, so behavior is unaffected — the doc now describes what the
code actually does instead of a stronger guarantee it doesn't implement.

Blast SHOULD-FIX 5: UiTemplateListBox.Flush()'s doc only mentioned the
ContentHeight reset; UiScrollablePanel.ClearContent() also resets scroll
position to 0, which the sibling UiItemList.Flush() (same method name,
different semantics) does NOT do. Documented explicitly, including the
UX cost this creates for a scrolled-in Friends/Squelch roster once its
scrollbar is wired (this fix round's blast MF-1) — flagged for whoever
revisits Friends/Squelch scrolling next rather than silently fixed as an
unasked behavior change.

Mechanism SHOULD-FIX 3: SocialPanelLiveMountProbeTests printed two
headline findings (the 0x10000492-authored-twice count, page exclusivity
after ActivateTabBehavior) without ever asserting them — a future
importer regression collapsing/dropping an instance, or breaking
exclusivity, could not fail this test. Both are now real assertions
(Assert.Equal(2, passupCount); exactly one page Visible and it is
Allegiance).

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

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

@@ -16,7 +16,9 @@ namespace AcDream.App.UI.Layout;
 /// <c>m_pFellowship == null</c>, and vice-versa. Both are AUTHORED sibling
 /// containers of the fellowship page (<c>0x10000292</c>) — confirmed by the
 /// FA3 live-mount probe: <c>0x1000026B</c> holds the name-entry box, Create
-/// button, and all three visible option checkboxes; <c>0x10000275</c> holds
+/// button, and all FOUR visible option checkboxes (Ignore Fellowship
+/// Requests / Auto-Accept Requests / Share XP / Share Loot —
+/// <c>0x10000270</c>–<c>0x10000273</c>, fix-round mechanism SF-4); <c>0x10000275</c> holds
 /// the roster list and all six member-management buttons. A single
 /// <see cref="UiElement.Visible"/> toggle on each container is therefore the
 /// WHOLE empty-state swap; no per-child hiding is needed (closes lane-A