feat(electrobun): port all Tauri features — full settings, popup menus, provider capabilities

New components (8):
- provider-capabilities.ts: per-provider feature flags (claude/codex/ollama)
- settings/AppearanceSettings.svelte: theme, fonts, cursor, scrollback
- settings/AgentSettings.svelte: shell, CWD, permissions, providers
- settings/SecuritySettings.svelte: keyring, secrets, branch policies
- settings/ProjectSettings.svelte: per-project provider/model/worktree/sandbox
- settings/OrchestrationSettings.svelte: wake strategy, notifications, anchors
- settings/AdvancedSettings.svelte: logging, OTLP, plugins, import/export

Updated:
- ChatInput: radial context indicator (78% demo, color-coded arc),
  4 popup menus (upload/context/web/slash), provider-gated icons
- SettingsDrawer: 6-category sidebar shell
- AgentPane: passes provider + contextPct to ChatInput

ui-electrobun/src/mainview/AgentPane.svelte

@@ -31,6 +31,8 @@
     costUsd,
     tokens,
     model = 'claude-opus-4-5',
+    provider = 'claude',
+    contextPct = 0,
     onSend,
   }: Props = $props();
 
@@ -178,6 +180,8 @@
     <ChatInput
       value={promptText}
       {model}
+      {provider}
+      {contextPct}
       onSend={handleSend}
       onInput={(v) => (promptText = v)}
     />