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.UI.Abstractions/Panels/Settings/CharacterSettings.cs

@@ -0,0 +1,48 @@
+namespace AcDream.UI.Abstractions.Panels.Settings;
+
+/// <summary>
+/// Per-character preferences persisted to <c>settings.json</c> under
+/// <c>character[toonName]</c>. Settings on this tab are scoped to a
+/// single toon; switching characters loads a different bag.
+///
+/// <para>
+/// L.0 scope: <b>local-only</b>. The settings here describe how the
+/// client UI behaves for the active toon — they don't yet flow to the
+/// server. When server-sync ships, options like <see cref="AutoAttack"/>
+/// would be pushed via the retail Player-Options packet.
+/// </para>
+///
+/// <para>
+/// MVP shape — four settings only. Easy to grow when more per-toon
+/// preferences land. Each is value-typed so equality and Cancel-revert
+/// behave like the other tabs' records.
+/// </para>
+/// </summary>
+public sealed record CharacterSettings(
+    string DefaultChatChannel,            // "Local" / "Allegiance" / "Fellowship" / "General" / etc.
+    bool   AutoAttack,                    // Tap-to-attack continues swinging until target dies
+    bool   ConfirmSalvage,                // Prompt before salvaging valuable items
+    bool   ShowPickupMessages)            // "You picked up X" lines in chat
+{
+    /// <summary>Defaults applied to a fresh character (no settings.json
+    /// entry yet). Conservative — opt-in for AutoAttack, opt-in for
+    /// confirmation prompts, pickup messages on by default.</summary>
+    public static CharacterSettings Default { get; } = new(
+        DefaultChatChannel: "Local",
+        AutoAttack:         false,
+        ConfirmSalvage:     true,
+        ShowPickupMessages: true);
+
+    /// <summary>Channel-name presets exposed in the dropdown. Order
+    /// roughly matches retail's chat-channel routing.</summary>
+    public static System.Collections.Generic.IReadOnlyList<string> AvailableChannels { get; } = new[]
+    {
+        "Local",
+        "Allegiance",
+        "Fellowship",
+        "General",
+        "Trade",
+        "LFG",
+        "Roleplay",
+    };
+}