ci(a11y): axe-core gate + accessibility-tree snapshots (#222)

e2e/a11y.spec.ts runs @axe-core/playwright (WCAG 2.x A/AA) over the login
page, room timeline + composer, message options menu, thread panel, user
settings and room settings, failing on critical/serious findings other
than colour contrast (reported, not gated: generated avatar colours and
portal false positives). Aria snapshots of the composer, message menu,
thread panel and settings nav catch lost names/roles/live regions.

Burned down what the first run found:
- NavItem: callers' aria-selected is not valid on a div (axe critical);
  it now drives data-selected for styling and aria-current="page".
- Composer placeholder at 0.5 opacity was ~2.3:1; now P300.
- Voice-limit and explore custom-limit number inputs had no label.
- Thread panel is an <aside aria-label="Thread">; the settings modal is a
  role=dialog; the settings sections are a <nav>; the message action
  menu carries data-message-menu + a label.

Also allows WebKit's CI wording for the well-known probe ("Could not
connect … Connection refused") that failed run #2003.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

package-lock.json

@@ -80,6 +80,7 @@
         "workbox-precaching": "7.4.1"
       },
       "devDependencies": {
+        "@axe-core/playwright": "4.13.0",
         "@lotusguild/element-call-embedded": "0.25.0-lotus.9",
         "@playwright/test": "1.63.0",
         "@rollup/plugin-inject": "5.0.5",
@@ -172,6 +173,19 @@
         "@babel/runtime": "^7.0.0"
       }
     },
+    "node_modules/@axe-core/playwright": {
+      "version": "4.13.0",
+      "resolved": "https://registry.npmjs.org/@axe-core/playwright/-/playwright-4.13.0.tgz",
+      "integrity": "sha512-6YLx+kxXu5GJceG4ozFg+33a2EMTdjYwWGloJ3sb9Kta5pp+ZNS53uxGVog5JetIY8s++P5UrtX+cri+u0VAVg==",
+      "dev": true,
+      "license": "MPL-2.0",
+      "dependencies": {
+        "axe-core": "~4.13.0"
+      },
+      "peerDependencies": {
+        "playwright-core": ">= 1.0.0"
+      }
+    },
     "node_modules/@babel/code-frame": {
       "version": "7.29.0",
       "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.29.0.tgz",
@@ -4847,10 +4861,11 @@
       }
     },
     "node_modules/axe-core": {
-      "version": "4.10.2",
-      "resolved": "https://registry.npmjs.org/axe-core/-/axe-core-4.10.2.tgz",
-      "integrity": "sha512-RE3mdQ7P3FRSe7eqCWoeQ/Z9QXrtniSjp1wUjt5nRC3WIpz5rSCve6o3fsZ2aCpJtrZjSZgjwXAoTO5k4tEI0w==",
+      "version": "4.13.0",
+      "resolved": "https://registry.npmjs.org/axe-core/-/axe-core-4.13.0.tgz",
+      "integrity": "sha512-UzGt8zg7Ny8djbYMhxl2zuEevVa7r2gJjYY5Lwr1xM7+XU2nd6CkIWFTVcCIbAP63vSz71NaVyyuSk9lHKcy0A==",
       "dev": true,
+      "license": "MPL-2.0",
       "engines": {
         "node": ">=4"
       }