feat(ui): Character tab — per-toon settings; Phase L.0 complete

Phase L.0 (final) — last tab on the Settings shell. Per-toon
preferences keyed by toon name in settings.json under
character[<toonName>]. With this commit the L.0 build order
finishes and every approved tab is implemented.

CharacterSettings record (4 fields):
 · DefaultChatChannel (string — Local / Allegiance / Fellowship / etc)
 · AutoAttack (bool — continue swinging until target dies)
 · ConfirmSalvage (bool — prompt before salvaging valuable items)
 · ShowPickupMessages (bool — pickup lines in chat)

AvailableChannels static list exposes the 7 retail-routing targets
for the dropdown.

SettingsStore grows LoadCharacter(toonKey) / SaveCharacter(toonKey)
using JsonNode/JsonObject for the nested-toon write — the existing
SaveSection raw-text-preservation pattern handles top-level keys
but doesn't fit the nested per-toon mutation. The character map
preserves every other toon's settings on save, and other top-level
sections (display / audio / gameplay / chat) are preserved too.

SettingsVM grows the parallel character state machine. The host
owns the toonKey (currently hard-coded to "default" in GameWindow
because we don't have a current-character source plumbed yet) —
the VM just edits whatever bag the host loaded.

SettingsPanel.RenderCharacterTab replaces the L.0-shell placeholder
— a Combo for default chat channel + 3 Checkboxes for
AutoAttack / ConfirmSalvage / ShowPickupMessages. The
RenderPlaceholder helper is now removed (no callers); the old
"Placeholder_tabs_render_coming_soon_text_when_active" test is
replaced by an "all six tabs are implemented" guard test that
fails if any future commit adds a placeholder back.

GameWindow loads/saves character settings under toonKey "default"
with a TODO comment to swap in the real toon name once
CharacterList plumbing exposes a currentCharacter source.

18 new tests:
 · CharacterSettings record (4) — defaults pinned, AvailableChannels
   list shape, value equality, with-expressions
 · SettingsStore character (6) — missing-file / toon-not-in-file →
   defaults, round-trip, multi-toon preservation, preserves other
   top-level sections, all five sections coexist
 · SettingsVM character (5) — initial draft, SetCharacter marks
   dirty, Save invokes callback, Cancel reverts, ResetAllToDefaults
   covers
 · SettingsPanel character tab (3 net, after removing the
   placeholder test) — combo+checkboxes render only when active,
   channel combo uses AvailableChannels, all six tabs are now
   non-placeholder

Phase L.0 final tally:
 · 5 commits on feature/settings-retail (shell + 5 tabs)
 · 6 tabs: Keybinds (Phase K) + Display + Audio + Gameplay + Chat + Character
 · 5 settings sections in settings.json (display/audio/gameplay/chat/character),
   coexisting non-destructively + a sixth file (keybinds.json) on the side.

dotnet build green (0 warnings); dotnet test 1,307 / 1,307 green
(243 Core.Net + 391 UI.Abstractions + 673 Core).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.UI.Abstractions.Tests/Panels/Settings/SettingsStoreTests.cs

@@ -284,4 +284,87 @@ public sealed class SettingsStoreTests : System.IDisposable
         Assert.False(store.LoadChat().HearTradeChat);
         Assert.Equal(14f, store.LoadChat().FontSize);
     }
+
+    // -- Character section round-trip (per-toon) --------------------------
+
+    [Fact]
+    public void LoadCharacter_returns_defaults_when_file_is_missing()
+    {
+        var store = new SettingsStore(_tempPath);
+        Assert.Equal(CharacterSettings.Default, store.LoadCharacter("default"));
+    }
+
+    [Fact]
+    public void LoadCharacter_returns_defaults_when_toonKey_not_in_file()
+    {
+        // File exists with a different toon's data; asking for "+Acdream"
+        // returns defaults rather than the other toon's data.
+        var store = new SettingsStore(_tempPath);
+        store.SaveCharacter("Bob", CharacterSettings.Default with { AutoAttack = true });
+
+        var loaded = store.LoadCharacter("+Acdream");
+        Assert.Equal(CharacterSettings.Default, loaded);
+    }
+
+    [Fact]
+    public void SaveCharacter_then_LoadCharacter_round_trips_all_fields()
+    {
+        var store = new SettingsStore(_tempPath);
+        var original = new CharacterSettings(
+            DefaultChatChannel: "Allegiance",
+            AutoAttack:         true,
+            ConfirmSalvage:     false,
+            ShowPickupMessages: false);
+
+        store.SaveCharacter("+Acdream", original);
+        Assert.Equal(original, store.LoadCharacter("+Acdream"));
+    }
+
+    [Fact]
+    public void SaveCharacter_preserves_other_toons_within_character_section()
+    {
+        // Two different toons, each with distinct settings — saving one
+        // must not clobber the other.
+        var store = new SettingsStore(_tempPath);
+        var alice = CharacterSettings.Default with { DefaultChatChannel = "Allegiance" };
+        var bob   = CharacterSettings.Default with { DefaultChatChannel = "Fellowship", AutoAttack = true };
+
+        store.SaveCharacter("Alice", alice);
+        store.SaveCharacter("Bob", bob);
+
+        Assert.Equal(alice, store.LoadCharacter("Alice"));
+        Assert.Equal(bob,   store.LoadCharacter("Bob"));
+    }
+
+    [Fact]
+    public void SaveCharacter_preserves_other_top_level_sections()
+    {
+        // Display/audio survive when SaveCharacter writes its nested map.
+        var store = new SettingsStore(_tempPath);
+        store.SaveDisplay(DisplaySettings.Default with { Resolution = "2560x1440" });
+        store.SaveAudio(AudioSettings.Default with { Master = 0.4f });
+        store.SaveCharacter("+Acdream", CharacterSettings.Default with { AutoAttack = true });
+
+        Assert.Equal("2560x1440", store.LoadDisplay().Resolution);
+        Assert.Equal(0.4f, store.LoadAudio().Master);
+        Assert.True(store.LoadCharacter("+Acdream").AutoAttack);
+    }
+
+    [Fact]
+    public void All_five_sections_coexist_in_one_settings_json()
+    {
+        var store = new SettingsStore(_tempPath);
+        store.SaveDisplay(DisplaySettings.Default with { Resolution = "2560x1440" });
+        store.SaveAudio(AudioSettings.Default with { Master = 0.5f });
+        store.SaveGameplay(GameplaySettings.Default with { LockUI = true });
+        store.SaveChat(ChatSettings.Default with { HearTradeChat = false });
+        store.SaveCharacter("+Acdream",
+            CharacterSettings.Default with { DefaultChatChannel = "Fellowship" });
+
+        Assert.Equal("2560x1440", store.LoadDisplay().Resolution);
+        Assert.Equal(0.5f, store.LoadAudio().Master);
+        Assert.True(store.LoadGameplay().LockUI);
+        Assert.False(store.LoadChat().HearTradeChat);
+        Assert.Equal("Fellowship", store.LoadCharacter("+Acdream").DefaultChatChannel);
+    }
 }