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>

src/AcDream.App/Rendering/GameWindow.cs

@@ -910,6 +910,13 @@ public sealed class GameWindow : IDisposable
                     var persistedAudio    = settingsStore.LoadAudio();
                     var persistedGameplay = settingsStore.LoadGameplay();
                     var persistedChat     = settingsStore.LoadChat();
+                    // Per-toon character settings keyed by name. We don't
+                    // know which toon the user will pick until after
+                    // CharacterList lands, so use a "default" bag for now.
+                    // Future: swap to the actual toon name once a
+                    // currentCharacter source is plumbed.
+                    const string toonKey = "default";
+                    var persistedCharacter = settingsStore.LoadCharacter(toonKey);
 
                     // Apply persisted audio to the engine BEFORE the panel
                     // host starts pushing per-frame so the first frame uses
@@ -1007,6 +1014,21 @@ public sealed class GameWindow : IDisposable
                             {
                                 Console.WriteLine($"settings: chat save failed: {ex.Message}");
                             }
+                        },
+                        persistedCharacter: persistedCharacter,
+                        onSaveCharacter: character =>
+                        {
+                            try
+                            {
+                                settingsStore.SaveCharacter(toonKey, character);
+                                Console.WriteLine(
+                                    $"settings: character[{toonKey}] saved to "
+                                    + AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath());
+                            }
+                            catch (Exception ex)
+                            {
+                                Console.WriteLine($"settings: character save failed: {ex.Message}");
+                            }
                         });
                     _settingsPanel = new AcDream.UI.Abstractions.Panels.Settings.SettingsPanel(_settingsVm);
                     _panelHost.Register(_settingsPanel);