feat(e2e): add Playwright browser test suite for web routes

solitaire_server/e2e/:
- smoke.spec.js: verifies /play-classic loads, exposes window.__FERROUS_DEBUG__
  bridge, keyboard parity (Space=draw, U=undo), debug failure report, and
  replay payload builder exports schema-v2 moves.
- gameplay_review.spec.js: HUD/controls render check, stock-click + undo
  player flow, draw-mode toggle, autonomous play invariant batch, and
  cycle-detection regression guard.
- cycle_metrics.js: headless cycle-rate analysis tool; run via
  `npm run review:cycles` with configurable policy, game count, and
  thresholds. Regression gate baked into package.json scripts.
- playwright.config.js: targets the local server at http://localhost:8080.
- package.json / package-lock.json: @playwright/test 1.60.0.

.gitea/workflows/web-e2e.yml:
- Runs on pushes to solitaire_server/, solitaire_wasm/, solitaire_core/,
  or Cargo changes. Starts the server binary, waits for /health, runs
  the full Playwright suite, uploads test-results/ on failure.

docs/testing-architecture.md: documents the three-tier test strategy
  (unit → Playwright smoke → cycle regression) and the __FERROUS_DEBUG__
  bridge contract.

scripts/update_quaternions_deps.sh: helper to bump the Quaternions
  registry deps (klondike, card_game) by version and run the full
  safety gate including deterministic replay checks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_server/e2e/playwright.config.js

@@ -0,0 +1,41 @@
+const path = require("path");
+const { defineConfig, devices } = require("@playwright/test");
+
+const serverPort = 4173;
+const repoRoot = path.resolve(__dirname, "../..");
+
+module.exports = defineConfig({
+    testDir: "./tests",
+    timeout: 30_000,
+    expect: {
+        timeout: 5_000,
+    },
+    fullyParallel: false,
+    retries: process.env.CI ? 2 : 0,
+    workers: process.env.CI ? 1 : undefined,
+    reporter: [["list"], ["html", { open: "never" }]],
+    use: {
+        baseURL: `http://127.0.0.1:${serverPort}`,
+        trace: "retain-on-failure",
+        screenshot: "only-on-failure",
+        video: "retain-on-failure",
+    },
+    projects: [
+        {
+            name: "chromium",
+            use: { ...devices["Desktop Chrome"] },
+        },
+    ],
+    webServer: {
+        command:
+            `SQLX_OFFLINE=true ` +
+            `DATABASE_URL=sqlite://ferrous-solitaire-e2e.db ` +
+            `JWT_SECRET=ferrous_solitaire_e2e_secret_32_chars_long ` +
+            `SERVER_PORT=${serverPort} ` +
+            `cargo run -p solitaire_server --quiet`,
+        cwd: repoRoot,
+        url: `http://127.0.0.1:${serverPort}/health`,
+        timeout: 120_000,
+        reuseExistingServer: !process.env.CI,
+    },
+});