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/tests/smoke.spec.js

@@ -0,0 +1,66 @@
+const { test, expect } = require("@playwright/test");
+
+test("play-classic loads and exposes debug bridge", async ({ page }) => {
+    await page.goto("/play-classic?seed=42");
+    await page.waitForFunction(() => typeof window.__FERROUS_DEBUG__ === "object");
+
+    const seed = await page.evaluate(() => window.__FERROUS_DEBUG__.seed());
+    expect(seed).toBe(42);
+
+    const legalMoves = await page.evaluate(() => window.__FERROUS_DEBUG__.legalMoves());
+    expect(Array.isArray(legalMoves)).toBeTruthy();
+});
+
+test("keyboard parity: Space draws and U undoes", async ({ page }) => {
+    await page.goto("/play-classic?seed=42");
+    await page.waitForFunction(
+        () =>
+            typeof window.__FERROUS_DEBUG__ === "object" &&
+            window.__FERROUS_DEBUG__.seed() !== null
+    );
+
+    const baselineHistoryLen = await page.evaluate(
+        () => window.__FERROUS_DEBUG__.moveHistory().length
+    );
+
+    await page.keyboard.press("Space");
+    await expect
+        .poll(async () => await page.evaluate(() => window.__FERROUS_DEBUG__.moveHistory().length))
+        .toBe(baselineHistoryLen + 1);
+
+    await page.keyboard.press("KeyU");
+    await expect
+        .poll(async () => await page.evaluate(() => window.__FERROUS_DEBUG__.moveHistory().length))
+        .toBe(baselineHistoryLen);
+});
+
+test("debug failure report contains replay diagnostics", async ({ page }) => {
+    await page.goto("/play-classic?seed=42");
+    await page.waitForFunction(() => typeof window.__FERROUS_DEBUG__ === "object");
+
+    const report = await page.evaluate(() => window.__FERROUS_DEBUG__.failureReport());
+    expect(report).not.toBeNull();
+    expect(typeof report.seed).toBe("number");
+    expect(Array.isArray(report.moveHistory)).toBeTruthy();
+    expect(Array.isArray(report.legalMoves)).toBeTruthy();
+    expect(report.currentState).toBeTruthy();
+    expect(report.invariants).toBeTruthy();
+});
+
+test("replay payload builder exports schema-v2 moves", async ({ page }) => {
+    await page.goto("/play-classic?seed=42");
+    await page.waitForFunction(() => typeof window.__FERROUS_DEBUG__ === "object");
+
+    await page.keyboard.press("Space");
+
+    await expect
+        .poll(async () => await page.evaluate(() => window.__FERROUS_DEBUG__.replayPayload() !== null))
+        .toBe(true);
+    const payload = await page.evaluate(() => window.__FERROUS_DEBUG__.replayPayload());
+    expect(payload.schema_version).toBe(2);
+    expect(payload.draw_mode).toMatch(/Draw(One|Three)/);
+    expect(payload.mode).toBe("Classic");
+    expect(Array.isArray(payload.moves)).toBeTruthy();
+    expect(payload.moves.length).toBeGreaterThan(0);
+    expect(payload.win_move_index).toBe(payload.moves.length - 1);
+});