fix(mosstank): unclickable button, empty skill list, dev font, and chat output

Four defects from the first in-world look, three of them with a definite root
cause rather than a plausible one.

**The Buff button did nothing.** Not a hit-testing problem -- the pointer found
the button perfectly. UiRoot's press handling asks the pressed widget whether
it owns the pointer; a widget that does not claim the press falls through to
"move the ancestor window", and a window drag returns early on release without
ever emitting a Click. UiButton and UiClickablePanel both override
HandlesClick for exactly this reason; UiSimpleButton never did. Latent since
that class was written, and invisible until it was put inside a draggable
window -- which is precisely what a markup plugin panel is.

Found by reproducing it headlessly through the real UiRoot dispatcher rather
than by reasoning about it: MarkupPanelClickTests drives press-and-release over
the button and asserts the bound action ran, with a separate test asserting the
pointer finds the button at all, so a future failure says which half broke.
My earlier guess -- that a modal at character select was swallowing the click
-- was wrong, and the screenshot of the panel live in world disproved it.

**"0 trained skills".** The skill-name table was read in OnLoad *before*
GameWindowCompositionPipeline.Run, which is what publishes the DAT collection,
so _dats was still null, the whole block was skipped, and the surface reported
an empty skill list with nothing to explain it. Bound in PublishDatCollection
instead -- the moment the data exists -- so it cannot run early again whatever
the phase ordering does, and a genuinely missing SkillTable now says so.

**Plugin text used the development bitmap font.** UiLabel and UiSimpleButton
gained a DatFont, and MarkupDocument now takes the retail interface font from
the host, so plugin panels render through the same glyph path (including
retail's two-plane outline) as authored panels.

**MossTank now writes to chat.** New BCL-only IPluginChat routes to retail's
ClientLocal log type (0x1A) -- the channel the client uses for its own notices,
local to this client, so a plugin cannot speak in the player's name. MossTank
announces the start, the finish with a cast count, and a stall.

Not addressed here: the cursor showing blue rather than amber. Traced but not
fixed -- CursorFeedbackController picks the cursor family from combat mode, and
CombatMode.Magic selects the blue Magic cursor where Default is amber. That is
a combat-mode question, unrelated to this change, and worth its own look rather
than a speculative fix folded in here.

Solution builds clean; 14,437 tests pass on the standard hermetic lane filter,
0 failures.

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

src/AcDream.Plugin.Abstractions/Automation.cs

@@ -127,6 +127,17 @@ public interface ISpellCatalog
     bool TryGet(uint spellId, out PluginSpellInfo info);
 }
 
+/// <summary>Writing to the player's chat window.</summary>
+public interface IPluginChat
+{
+    /// <summary>
+    /// Post a client-local system line, the channel retail uses for the
+    /// client's own notices. It is local to this client: nothing is sent to the
+    /// server and no other player sees it.
+    /// </summary>
+    void PostSystemMessage(string text);
+}
+
 /// <summary>Casting, with a preflight so a plugin need not guess.</summary>
 public interface IMagicCommands
 {
@@ -158,6 +169,7 @@ public interface IAutomationSurface
     ICharacterInfo Character { get; }
     ISpellCatalog Spells { get; }
     IMagicCommands Magic { get; }
+    IPluginChat Chat { get; }
 }
 
 /// <summary>
@@ -165,7 +177,7 @@ public interface IAutomationSurface
 /// and every command refuses, so a plugin can keep one code path.
 /// </summary>
 public sealed class NoOpAutomationSurface
-    : IAutomationSurface, ICharacterInfo, ISpellCatalog, IMagicCommands
+    : IAutomationSurface, ICharacterInfo, ISpellCatalog, IMagicCommands, IPluginChat
 {
     public static NoOpAutomationSurface Instance { get; } = new();
 
@@ -177,6 +189,11 @@ public sealed class NoOpAutomationSurface
     public ICharacterInfo Character => this;
     public ISpellCatalog Spells => this;
     public IMagicCommands Magic => this;
+    public IPluginChat Chat => this;
+
+    public void PostSystemMessage(string text)
+    {
+    }
 
     public bool IsInWorld => false;
     public uint CurrentHealth => 0;