fix(embed): video sizing letterbox and logo accent

- Changed embed video sizing to `object-fit: cover` and `width: 100%` to eliminate black bars/letterboxing.
- Updated `embed.html` and `css/tailwind.source.css` to enforce these styles on `.video-modal__media`, `.video-modal__video`, and `#embedVideo`.
- Wired the embed logo accent color to use the instance configuration (`THEME_ACCENT_OVERRIDES` from `config/instance-config.js`) via a `--bitvid-accent` CSS variable injected in `js/embed.js`.
- Added unit and visual tests to verify styling and configuration logic.

tests/visual/embed-layout.spec.ts

@@ -0,0 +1,41 @@
+import { expect, test } from "@playwright/test";
+import { THEME_ACCENT_OVERRIDES } from "../../config/instance-config.js";
+
+test.describe("embed layout and styling", () => {
+  test("embed video fills container and uses accent color", async ({ page }) => {
+    // Navigate to embed.html with a dummy pointer to trigger logic
+    await page.goto("/embed.html?pointer=nevent123", { waitUntil: "domcontentloaded" });
+
+    // 1. Verify CSS Variable
+    const accentColor = await page.evaluate(() => {
+      return getComputedStyle(document.documentElement).getPropertyValue("--bitvid-accent").trim();
+    });
+    // The configured color is #540011 (from config/instance-config.js)
+    const expectedAccent = THEME_ACCENT_OVERRIDES?.light?.accent || "#ff6b6b";
+    expect(accentColor).toBe(expectedAccent);
+
+    // 2. Verify Video Element Styling
+    const video = page.locator("#embedVideo");
+    await expect(video).toBeVisible();
+
+    const objectFit = await video.evaluate((el) => {
+      return window.getComputedStyle(el).objectFit;
+    });
+    expect(objectFit).toBe("cover");
+
+    const backgroundColor = await video.evaluate((el) => {
+      return window.getComputedStyle(el).backgroundColor;
+    });
+    // Transparent is typically rgba(0, 0, 0, 0)
+    expect(backgroundColor).toMatch(/rgba\(0,\s*0,\s*0,\s*0\)|transparent/);
+
+    // 3. Verify Logo Styling
+    const logoAccent = page.locator(".bv-logo__accent");
+    const fill = await logoAccent.evaluate((el) => {
+      return window.getComputedStyle(el).fill;
+    });
+
+    // #540011 in rgb is rgb(84, 0, 17)
+    expect(fill).toBe("rgb(84, 0, 17)");
+  });
+});