chore(plugins): remove the Smoke gate plugin; MossTank shelf icon 0x06002C41

Owner direction 2026-09-06: the owner visually accepted all three connected
gates from the plugin-shelf/DAT-icon work — the movable plugin shelf
(Slice A), the DAT icon markup (Slice B), and the retained-UI outline-order
fix (761a7519f). With that gate passed, the Smoke plugin's job as the gate
artifact is done, so it is deleted outright rather than merely hidden:
src/AcDream.Plugins.Smoke/ (SmokePlugin.cs, SmokeIconPanel.cs, csproj, lock
files).

Reference sites cleaned:
- AcDream.slnx: removed the project entry.
- src/AcDream.App/AcDream.App.csproj: removed the Smoke ProjectReference and
  the CopySmokePluginToBuildOutput/CopySmokePluginToPublishOutput targets;
  the MossTank equivalents are untouched.
- .github/workflows/headless-portability.yml: the Linux package-contract
  step no longer asserts a Smoke plugin.dll/plugin.json pair — repointed at
  MossTank's, since the step's job was to prove the plugin-copy packaging
  mechanism works end to end, not specifically to prove Smoke.
- tests/AcDream.Core.Tests/Plugins/PluginManifestTests.cs: the inline JSON
  fixture used Smoke's manifest values as arbitrary test data; swapped for
  MossTank's so the parser test still proves the same thing.
- tests/AcDream.App.Tests/Rendering/LinuxPlatformBoundaryTests.cs: the
  shipped-plugin-copy shape test counted 4 GetTargetPath targets (Smoke +
  MossTank, build + publish); now 2 (MossTank only).
- tests/AcDream.App.Tests/Plugins/AppAutomationSurfaceIconInstalledDatTests.cs:
  reworded a doc comment that named the now-deleted SmokeIconPanel.
- README.md, docs/plugin-ui-markup.md: dropped Smoke-specific mentions,
  kept the icon markup example/grammar (now citing MossTank's own real
  IconSurfaceId).
- docs/plans/2026-09-06-plugin-shelf-and-dat-icons.md: recorded the owner's
  2026-09-06 acceptance and the Smoke removal in the review ledger; deleted
  the now-moot "before shipment" Smoke-in-release-zip warning.
- docs/reviews/coverage-ledger.md, docs/reviews/findings-ledger.md: left
  untouched — both are frozen audit snapshots ("complete for baseline
  <hash>"), so their Smoke rows are historical record, not live claims.
- docs/ISSUES.md: left untouched — its Smoke mentions are inside closed
  issue #193's historical write-up of a past investigation.

MossTank plugin shelf icon: MossTankPlugin.cs's PluginPanelDescriptor now
sets IconSurfaceId = 0x06002C41 (IconText = "MT" remains the fallback).
Verified against the installed retail DAT with a new InstalledDat-lane test,
tests/AcDream.App.Tests/UI/MossTankIconInstalledDatTests.cs, mirroring
RetailMarkupIconResolverInstalledDatTests's convention: confirms the id is a
real Portal/HighRes RenderSurface and that RetailMarkupIconResolver.ResolveDid
returns a non-zero texture for it.

Verified: dotnet build AcDream.slnx -c Release green; a stale
plugins/AcDream.Plugins.Smoke output folder from a prior build was deleted
and a fresh build does not recreate it. Full App suite: 7,363 passed / 97
skipped / 36 failed (was 7,362/97/36) — the failing set is unchanged and
none are plugin-related; the one new pass is the MossTank DAT-icon test.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/plugin-ui-markup.md

@@ -21,8 +21,8 @@ icon, and the parser that turns markup into a live `UiElement` tree
 host.Ui.AddPanel(
     new PluginPanelDescriptor("main", "MossTank")
     {
-        IconText = "MT",           // fallback initials if IconSurfaceId is 0
-        IconSurfaceId = 7735,      // Decal-style bare index OR a full DID — both normalize
+        IconText = "MT",             // fallback initials if IconSurfaceId is 0
+        IconSurfaceId = 0x06002C41,  // Decal-style bare index OR a full DID — both normalize
         StartVisible = true,
         ShowInSidePanel = true,
     },
@@ -32,9 +32,8 @@ host.Ui.AddPanel(
 
 `RegisterPanel` (same signature, returns `IDisposable`) removes the window
 independently of the plugin's own lifetime. `RegisterPanelContent` takes an
-in-memory KSML string instead of a file path — the route `AcDream.Plugins.Smoke`
-uses for its icon-surface proof panel (`SmokeIconPanel.cs`), when a panel is
-small enough not to need its own shipped `.xml` asset.
+in-memory KSML string instead of a file path — the route to reach for when a
+panel is small enough not to need its own shipped `.xml` asset.
 
 Every registered window gets a stable persisted key
 (`plugin:{pluginId}:{windowId}`), drag, resize (where the markup opts in),
@@ -263,9 +262,7 @@ There is no way to mix kinds within a single list. Two consequences:
   that wants the badge look has no `did`-space escape hatch.
 
 MosswartMassacre-style example — a list column composited from spell ids,
-with the spell's own raw art DID printed alongside the name for comparison
-(`AcDream.Plugins.Smoke`'s own proof panel, `SmokeIconPanel.cs`, is exactly
-this pattern):
+with the spell's own raw art DID printed alongside the name for comparison:
 
 ```csharp
 // iconkind="spell": the values MUST be spell ids (what ResolveSpell composites