refactor(import): add v4section/v4url aliases, inline clamp wrappers, replace classes with fns

Finding 5: Introduce V4Url + V4Section<T> type aliases in reactive-resume-v4-json.tsx; collapse
310-line V4ResumeData type (13x 5-field section header, 11x {label,href}) into typed aliases.
Inferred shape is structurally identical.

Finding 6: Remove 9 single-caller clamp/pxToPt wrappers; replace compile-time constants
(rotation=0, sidebarWidth=35, shadowWidth=0, gapX=4, gapY=6) with literals; inline dynamic
calls (clamp(x, 32, 512) etc.) at the two body/heading typography call sites.

Finding 7: Convert three stateless single-method importer classes to plain functions.
Extract shared rethrowAsImportError() to error.ts, replacing triplicated ZodError catch blocks.
Update web import dialog + all in-package test files to use function API.

Claude-Session: https://claude.ai/code/session_012Bnvt1MghwHj4qQRxuQUGa

packages/import/src/reactive-resume-json.test.ts

@@ -1,29 +1,27 @@
 import { describe, expect, it } from "vitest";
 import { defaultResumeData } from "@reactive-resume/schema/resume/default";
-import { ReactiveResumeJSONImporter } from "./reactive-resume-json";
+import { parseReactiveResumeJSON } from "./reactive-resume-json";
 
-const importer = new ReactiveResumeJSONImporter();
-
-describe("ReactiveResumeJSONImporter", () => {
+describe("parseReactiveResumeJSON", () => {
 	it("round-trips the default resume data", () => {
-		const result = importer.parse(JSON.stringify(defaultResumeData));
+		const result = parseReactiveResumeJSON(JSON.stringify(defaultResumeData));
 		expect(result.basics.name).toBe(defaultResumeData.basics.name);
 	});
 
 	it("throws a JSON-serialised validation error for an invalid object", () => {
 		// Missing required top-level fields.
-		expect(() => importer.parse(JSON.stringify({ foo: "bar" }))).toThrow();
+		expect(() => parseReactiveResumeJSON(JSON.stringify({ foo: "bar" }))).toThrow();
 	});
 
 	it("throws when the input is not valid JSON", () => {
-		expect(() => importer.parse("not-json")).toThrow();
+		expect(() => parseReactiveResumeJSON("not-json")).toThrow();
 	});
 
 	it("creates a default layout page when the imported data has no pages", () => {
 		const data = structuredClone(defaultResumeData);
 		data.metadata.layout.pages = [];
 
-		const result = importer.parse(JSON.stringify(data));
+		const result = parseReactiveResumeJSON(JSON.stringify(data));
 		expect(result.metadata.layout.pages.length).toBe(1);
 		expect(result.metadata.layout.pages[0]?.main.length).toBeGreaterThan(0);
 	});
@@ -38,7 +36,7 @@ describe("ReactiveResumeJSONImporter", () => {
 			},
 		];
 
-		const result = importer.parse(JSON.stringify(data));
+		const result = parseReactiveResumeJSON(JSON.stringify(data));
 		const firstPage = result.metadata.layout.pages[0];
 		expect(firstPage).toBeDefined();
 		const allIds = new Set([...(firstPage?.main ?? []), ...(firstPage?.sidebar ?? [])]);
@@ -53,7 +51,7 @@ describe("ReactiveResumeJSONImporter", () => {
 	});
 
 	it("does not modify the layout when every built-in section is already placed", () => {
-		const result = importer.parse(JSON.stringify(defaultResumeData));
+		const result = parseReactiveResumeJSON(JSON.stringify(defaultResumeData));
 		expect(result.metadata.layout.pages.length).toBe(defaultResumeData.metadata.layout.pages.length);
 	});
 });