feat(feed): compress the toolbar chip groups into labeled FilterSelect dropdowns

Adds a reusable FilterSelect: a "Label: value ▾" pill that opens a listbox (a checkmark
row for single-select, a checkbox row for multi), on the AnchoredPopover platform. It
replaces the two feed-toolbar chip walls:
  - Watch state (single-select, default All) — picking a row replaces + closes.
  - Content types (multi-select, default Normal; requireOne keeps at least one on) — rows
    toggle and the panel stays open.
The trigger summarises multi picks as "First +N". The component is source-agnostic, meant
for reuse anywhere a small known option set currently renders as a chip group.

FilterSelect takes a `testId` → the trigger gets it, each option gets `${testId}-${value}`,
so the feed/channel E2Es keep stable selectors. They now open the dropdown and assert the
option's aria-selected instead of the old inline aria-pressed chips (new expectContentType/
toggleContentType helpers).

frontend/e2e/channel.spec.ts

@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { clickVisibleChannelLink, openApp } from "./helpers";
+import { clickVisibleChannelLink, expectContentType, openApp, toggleContentType } from "./helpers";
 
 // Locks channel-view entry + exit: opening a channel from a feed card replaces the view, and
 // both the in-page Back and the browser Back return to the feed. (This orthogonal channel branch
@@ -68,29 +68,22 @@ test.describe("channel view", () => {
   }) => {
     await openApp(page);
     await expect(page.getByTestId("video-card").first()).toBeVisible();
-    const feedLive = page.getByTestId("feed-content-includeLive");
-    await expect(feedLive).toHaveAttribute("aria-pressed", "false");
+    await expectContentType(page, "includeLive", false);
 
     // Inherit OFF: the channel toolbar's Live/Upcoming stays off, not forced on.
     await page.getByTestId("video-card-channel").first().click();
     await expect(page.getByTestId("channel-title")).toBeVisible();
-    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute(
-      "aria-pressed",
-      "false",
-    );
+    await expectContentType(page, "includeLive", false);
     await page.getByTestId("channel-back").click();
     await expect(page.getByTestId("channel-title")).toHaveCount(0);
 
     // Inherit ON: flip the feed's Live/Upcoming on, reopen the channel → it inherits the on state.
-    await feedLive.click();
-    await expect(feedLive).toHaveAttribute("aria-pressed", "true");
+    await toggleContentType(page, "includeLive");
+    await expectContentType(page, "includeLive", true);
     await expect(page.getByTestId("video-card").first()).toBeVisible();
     await page.getByTestId("video-card-channel").first().click();
     await expect(page.getByTestId("channel-title")).toBeVisible();
-    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute(
-      "aria-pressed",
-      "true",
-    );
+    await expectContentType(page, "includeLive", true);
   });
 
   // Bug 2 (Platform S5): the channel view is its OWN filter scope — a content toggle made there
@@ -99,27 +92,18 @@ test.describe("channel view", () => {
   test("a channel's content toggle does not leak into the feed", async ({ page }) => {
     await openApp(page);
     await expect(page.getByTestId("video-card").first()).toBeVisible();
-    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute(
-      "aria-pressed",
-      "false",
-    );
+    await expectContentType(page, "includeLive", false);
 
     // Turn Live/Upcoming ON inside the channel view.
     await page.getByTestId("video-card-channel").first().click();
     await expect(page.getByTestId("channel-title")).toBeVisible();
-    await page.getByTestId("feed-content-includeLive").click();
-    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute(
-      "aria-pressed",
-      "true",
-    );
+    await toggleContentType(page, "includeLive");
+    await expectContentType(page, "includeLive", true);
 
     // Back on the feed, its Live/Upcoming is still off — the channel's change stayed local.
     await page.getByTestId("channel-back").click();
     await expect(page.getByTestId("channel-title")).toHaveCount(0);
-    await expect(page.getByTestId("feed-content-includeLive")).toHaveAttribute(
-      "aria-pressed",
-      "false",
-    );
+    await expectContentType(page, "includeLive", false);
   });
 
   // Platform S4b: the whole channel chrome (banner, identity, tabs, toolbar) is fixed — it stays