refactor: organize frontend components into features/ directories

Moved 43 component files into 9 feature domains:
- features/git/ — commit-dialog, commit-panel, file-editor, git-mount-editor,
  git-toolbar, merge-dialog
- features/project/ — repositories-settings-tab, repository-create-dialog
- features/terminal/ — special-keys-panel, special-keys-strip,
  terminal-session-tabs, terminal
- features/workspace/ — workspace-card, workspace-create-form,
  workspace-header, workspace-instance-chips
- features/session/ — create-session-form, session-card, session-list
- features/tool/ — instance-list, manifest-editor, start-tool-fab,
  start-tool-modal, tool-starter, tools-bottom-sheet
- features/notification/ — event-toast-bridge, notification-center,
  notification-item
- features/settings/ — settings-tab-layout
- features/mobile/ — mobile-action-sheet, mobile-detail-view, mobile-edit-view,
  mobile-fab, mobile-list-view, mobile-nav, mobile-page-header,
  mobile-terminal-header, mobile-terminal-wrapper

Updated all imports across pages and components.
Root components/ now only contains generic UI pieces:
app-shell, code-editor, data-states, icon, protected-route, syntax-highlighter.

Quality gates: verified no remaining old imports.

apps/web/src/pages/WorkspacesPage.tsx

@@ -4,9 +4,9 @@ import { useState } from "react";
 import { Icon } from "../components/icon";
 import { useWorkspaces } from "../hooks/use-workspaces";
 import { useWorkspaceActions } from "../hooks/use-workspace-actions";
-import { WorkspaceCard } from "../components/workspace-card";
-import { WorkspaceCreateForm } from "../components/workspace-create-form";
-import { ToolStarter } from "../components/tool-starter";
+import { WorkspaceCard } from "../components/features/workspace/workspace-card";
+import { WorkspaceCreateForm } from "../components/features/workspace/workspace-create-form";
+import { ToolStarter } from "../components/features/tool/tool-starter";
 import type { Workspace } from "../types/workspace";
 
 export function WorkspacesPage() {