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/provider-capabilities.ts

@@ -0,0 +1,45 @@
+export type ProviderId = 'claude' | 'codex' | 'ollama';
+
+export interface ProviderCapabilities {
+  upload: boolean;
+  context: boolean;
+  web: boolean;
+  slash: boolean;
+  images: boolean;
+  defaultModel: string;
+  label: string;
+}
+
+export const PROVIDER_CAPABILITIES: Record<ProviderId, ProviderCapabilities> = {
+  claude: {
+    upload: true,
+    context: true,
+    web: true,
+    slash: true,
+    images: true,
+    defaultModel: 'claude-opus-4-5',
+    label: 'Claude',
+  },
+  codex: {
+    upload: true,
+    context: true,
+    web: false,
+    slash: true,
+    images: false,
+    defaultModel: 'gpt-5.4',
+    label: 'Codex',
+  },
+  ollama: {
+    upload: false,
+    context: true,
+    web: false,
+    slash: true,
+    images: false,
+    defaultModel: 'qwen3:8b',
+    label: 'Ollama',
+  },
+};
+
+export function getCapabilities(provider: string): ProviderCapabilities {
+  return PROVIDER_CAPABILITIES[provider as ProviderId] ?? PROVIDER_CAPABILITIES.claude;
+}