feat: support multiple image uploads for AI event generation 🖼️

- Updated OpenRouter integration to accept an array of image URLs
- Updated ImagePicker to use the `multiple` attribute natively
- Added `appendImagesDeduped` for handling client-side image deduplication
- Enhanced clipboard pasting to extract multiple images at once
- Rendered multiple images in a horizontal thumbnail strip in the AIToolbar
- Added tests to cover multi-image logic and AI request mapping

tests/multi-image.test.ts

@@ -0,0 +1,103 @@
+import { describe, expect, test } from "bun:test";
+import {
+	appendImagesDeduped,
+	imageFileKey,
+} from "@/lib/multi-image";
+
+// ---------------------------------------------------------------------------
+// Multi-image helpers – behavioral tests
+//
+// These functions are pure; they own the "append + dedup" contract.
+// Tests describe what the system DOES, not how it's implemented.
+// ---------------------------------------------------------------------------
+
+describe("imageFileKey – stable identity for dedup", () => {
+	test("returns a string combining name and size", () => {
+		const file = new File(["hello"], "flyer.png", { type: "image/png" });
+		const key = imageFileKey(file);
+		expect(typeof key).toBe("string");
+		expect(key).toContain("flyer.png");
+		expect(key).toContain(String(file.size));
+	});
+
+	test("two files with the same name and size produce the same key", () => {
+		const a = new File(["hello"], "a.png", { type: "image/png" });
+		const b = new File(["hello"], "a.png", { type: "image/png" });
+		expect(imageFileKey(a)).toBe(imageFileKey(b));
+	});
+
+	test("two files with the same name but different content produce different keys", () => {
+		const a = new File(["hello"], "a.png", { type: "image/png" });
+		const b = new File(["hello world"], "a.png", { type: "image/png" });
+		expect(imageFileKey(a)).not.toBe(imageFileKey(b));
+	});
+
+	test("two files with different names but same content produce different keys", () => {
+		const a = new File(["hello"], "a.png", { type: "image/png" });
+		const b = new File(["hello"], "b.png", { type: "image/png" });
+		expect(imageFileKey(a)).not.toBe(imageFileKey(b));
+	});
+});
+
+describe("appendImagesDeduped – append with deduplication", () => {
+	const makeFile = (name: string, content = "data") =>
+		new File([content], name, { type: "image/png" });
+
+	test("appends new files to an empty list", () => {
+		const result = appendImagesDeduped([], [makeFile("a.png")]);
+		expect(result).toHaveLength(1);
+		expect(result[0].name).toBe("a.png");
+	});
+
+	test("appends new files to an existing list", () => {
+		const existing = [makeFile("a.png")];
+		const incoming = [makeFile("b.png")];
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result).toHaveLength(2);
+		expect(result.map((f) => f.name)).toEqual(["a.png", "b.png"]);
+	});
+
+	test("silently ignores incoming files that are exact duplicates (same name+size)", () => {
+		const existing = [makeFile("a.png")];
+		const incoming = [makeFile("a.png")]; // identical name + content = same size
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result).toHaveLength(1);
+		expect(result[0].name).toBe("a.png");
+	});
+
+	test("appends non-duplicate files even when some duplicates are in the batch", () => {
+		const existing = [makeFile("a.png")];
+		const incoming = [makeFile("a.png"), makeFile("b.png")];
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result).toHaveLength(2);
+		expect(result.map((f) => f.name)).toEqual(["a.png", "b.png"]);
+	});
+
+	test("preserves existing list order — new files are appended at the end", () => {
+		const existing = [makeFile("first.png"), makeFile("second.png")];
+		const incoming = [makeFile("third.png")];
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result.map((f) => f.name)).toEqual([
+			"first.png",
+			"second.png",
+			"third.png",
+		]);
+	});
+
+	test("returns a new array (does not mutate the existing list)", () => {
+		const existing = [makeFile("a.png")];
+		const incoming = [makeFile("b.png")];
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result).not.toBe(existing); // new reference
+		expect(existing).toHaveLength(1); // original untouched
+	});
+
+	test("handles multiple incoming files with internal duplicates", () => {
+		// Two identical files in the same incoming batch
+		const existing: File[] = [];
+		const incoming = [makeFile("a.png"), makeFile("a.png"), makeFile("b.png")];
+		const result = appendImagesDeduped(existing, incoming);
+		expect(result).toHaveLength(2);
+		expect(result.map((f) => f.name)).toEqual(["a.png", "b.png"]);
+	});
+});