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/components/features/tool/start-tool-modal.tsx

@@ -0,0 +1,114 @@
+/** Modal for starting a tool on a workspace. */
+
+import { useState } from "react";
+import { Icon } from "./icon";
+import { listToolTypes, type ToolType } from "../api/tool-types";
+import { useAsyncData } from "../hooks/use-async-data";
+import type { Workspace } from "../types/workspace";
+
+export interface StartToolModalProps {
+	workspace: Workspace;
+	onClose: () => void;
+	onStart: (toolTypeId: string, configProfileId?: string) => Promise<void>;
+}
+
+export function StartToolModal({
+	workspace,
+	onClose,
+	onStart,
+}: StartToolModalProps) {
+	const [toolTypeId, setToolTypeId] = useState("");
+	const [configProfileId, setConfigProfileId] = useState("");
+	const [submitting, setSubmitting] = useState(false);
+	const [error, setError] = useState<string | null>(null);
+
+	const {
+		data: toolTypes,
+		status,
+		error: loadError,
+	} = useAsyncData<ToolType[]>(listToolTypes, []);
+
+	const handleSubmit = async (e: React.FormEvent) => {
+		e.preventDefault();
+		if (!toolTypeId) {
+			setError("Please select a tool type");
+			return;
+		}
+		setSubmitting(true);
+		setError(null);
+		try {
+			await onStart(toolTypeId, configProfileId || undefined);
+			onClose();
+		} catch (err) {
+			setError(err instanceof Error ? err.message : "Failed to start tool");
+		} finally {
+			setSubmitting(false);
+		}
+	};
+
+	return (
+		<div className="modal-overlay" onClick={onClose}>
+			<div className="modal-content" onClick={(e) => e.stopPropagation()}>
+				<div className="modal-header">
+					<h3>
+						<Icon name="play" size="sm" /> Start Tool on {workspace.name}
+					</h3>
+					<button className="btn btn-icon" onClick={onClose}>
+						<Icon name="cancel" size="sm" />
+					</button>
+				</div>
+				<form onSubmit={handleSubmit}>
+					<div className="form-group">
+						<label htmlFor="tool-type">Tool Type</label>
+						<select
+							id="tool-type"
+							value={toolTypeId}
+							onChange={(e) => setToolTypeId(e.target.value)}
+							disabled={submitting || status === "loading"}
+						>
+							<option value="">Select a tool...</option>
+							{toolTypes?.map((tt) => (
+								<option key={tt.id} value={tt.id}>
+									{tt.display_name}
+								</option>
+							))}
+						</select>
+						{status === "loading" && (
+							<span className="muted">Loading tools...</span>
+						)}
+						{loadError && <span className="error-text">{loadError}</span>}
+					</div>
+					<div className="form-group">
+						<label htmlFor="config-profile">Config Profile (optional)</label>
+						<input
+							id="config-profile"
+							type="text"
+							value={configProfileId}
+							onChange={(e) => setConfigProfileId(e.target.value)}
+							placeholder="Profile ID"
+							disabled={submitting}
+						/>
+					</div>
+					{error && <p className="form-error">{error}</p>}
+					<div className="form-actions">
+						<button
+							type="button"
+							className="btn btn-secondary"
+							onClick={onClose}
+							disabled={submitting}
+						>
+							Cancel
+						</button>
+						<button
+							type="submit"
+							className="btn btn-primary"
+							disabled={submitting || status !== "ready"}
+						>
+							{submitting ? "Starting..." : "Start Tool"}
+						</button>
+					</div>
+				</form>
+			</div>
+		</div>
+	);
+}