Fix sidebar rail overflow on the chat page

The content offset was fine — the rail's glass panel was the problem. As a
flex-1 item in the row-flex aside, the panel's automatic minimum size
(min-width: auto) is its content's min-content width. The chat list's
search input (an <input> defaults to size=20) has a ~192px intrinsic
width, which with the New chat button stretched the panel to 345px — 89px
past the 268px rail — where it painted over the chat page: the header
title, the composer placeholder ("sk about your notes...") and the
context chip ("ts").

- min-w-0 on the panel so the rail width always wins and wide content
  truncates instead (the input and list rows already shrink/truncate).
- Chat suite: assert the panel stays inside the rail and the main content
  starts after it, expanded and collapsed (the old checks counted
  elements, never their boxes — this is what slipped through).
- README: history bullet + decision 49. SW -> freezmo-v36.

Verified on the dev instance and a production build: panel 244px inside
the 268px rail (60px in the 84px collapsed rail) at 1024-1920, content
starts after the rail, all sidebar pages unchanged, dark + light, and
the full e2e (12/12 suites, 516 checks).

tests/chat-test.mjs

@@ -256,6 +256,38 @@ try {
     await desktop.page.waitForTimeout(1200);
     check("desktop: chat route opens with the sidebar", desktop.page.url().endsWith("/chat") && (await desktop.page.locator("aside").count()) >= 1);
     check("desktop: no tab bar on chat", (await desktop.page.locator("nav.tabbar").count()) === 0);
+
+    /* The rail must not paint over the page: its glass panel stays inside the
+       rail and the chat content starts after it. Regression: a wide chat list
+       stretched the panel (flex item min-width: auto) past the rail and
+       covered the header title, composer and context chip. */
+    const railMetrics = () =>
+      desktop.page.evaluate(() => {
+        const aside = document.querySelector("aside[aria-label]");
+        const panel = aside?.firstElementChild;
+        const main = document.querySelector("main");
+        if (!aside || !panel || !main) return null;
+        const a = aside.getBoundingClientRect();
+        const p = panel.getBoundingClientRect();
+        const m = main.getBoundingClientRect();
+        return {
+          panelInside: p.right <= a.right - 1,
+          contentClear: m.left >= a.right - 1,
+          gap: Math.round(m.left - p.right),
+          overflowing: [...panel.querySelectorAll("*")].some((el) => el.getBoundingClientRect().right > p.right + 1),
+        };
+      });
+
+    const expandedRail = await railMetrics();
+    check("desktop: sidebar panel stays inside the rail", expandedRail !== null && expandedRail.panelInside && !expandedRail.overflowing);
+    check("desktop: chat content starts after the sidebar", expandedRail !== null && expandedRail.contentClear && expandedRail.gap > 0);
+
+    await desktop.page.getByRole("button", { name: "Collapse sidebar" }).click();
+    await desktop.page.waitForTimeout(400);
+    const collapsedRail = await railMetrics();
+    check("desktop: collapsed rail also stays inside and clear", collapsedRail !== null && collapsedRail.panelInside && !collapsedRail.overflowing && collapsedRail.contentClear);
+    await desktop.page.getByRole("button", { name: "Expand sidebar" }).click();
+    await desktop.page.waitForTimeout(400);
     await desktop.context.close();
 
     const phone = await makePage(browser);