Move the e2e suites into the repo (tests/), out of /tmp

The browser harness lived in /tmp/opencode and an overnight reboot
wiped it. It now lives in tests/ and survives reboots, is versioned
and runs with one command.

- tests/lib.mjs: shared helpers (Chromium auto-detect, seeding,
  IndexedDB fixtures, stub/extra instance spawn with process-group
  cleanup, check/finish).
- tests/run-all.mjs + npm run test:e2e [filter]: runs the ten suites
  in order with a summary; suites that need a stub Ollama or VAPID
  keys start their own next start instance on 3208/3209, verify the
  port is free and kill the group on exit. Test scratch in
  tests/.tmp/ (gitignored).
- Suites rebuilt and green against the current build: regression 38,
  mobile 94 (tab matrix, ... sheet, settings sheet, axe), wizard 83,
  native 31 (PWA/offline/share/back/undo/haptics/draft), i18n 13,
  freeze-loading 6, review 15, phase1 36 (backup/sync/usage limits),
  phase2 42 (learning engine/reminders), phase3 21 (homework check).
  379 checks, 10/10 suites in one full run.
- playwright-core + axe-core added as devDependencies; CHROME env or
  the newest ~/.cache/ms-playwright chromium is used.
- README: new decision 45 documenting the harness; decision 44's
  verification note updated.

The older suites' exact sources were lost with the wipe, so the
rebuilt versions reconstruct the same feature areas rather than
being byte-identical.

package-lock.json

@@ -27,8 +27,10 @@
         "@types/react": "^19",
         "@types/react-dom": "^19",
         "@types/web-push": "^3.6.4",
+        "axe-core": "^4.14.0",
         "eslint": "^9",
         "eslint-config-next": "15.5.27",
+        "playwright-core": "^1.64.0",
         "tailwindcss": "^4",
         "typescript": "^5"
       }
@@ -2697,9 +2699,9 @@
       }
     },
     "node_modules/axe-core": {
-      "version": "4.13.0",
-      "resolved": "https://registry.npmjs.org/axe-core/-/axe-core-4.13.0.tgz",
-      "integrity": "sha512-UzGt8zg7Ny8djbYMhxl2zuEevVa7r2gJjYY5Lwr1xM7+XU2nd6CkIWFTVcCIbAP63vSz71NaVyyuSk9lHKcy0A==",
+      "version": "4.14.0",
+      "resolved": "https://registry.npmjs.org/axe-core/-/axe-core-4.14.0.tgz",
+      "integrity": "sha512-9WTZxEjsZ7b13TH8JPmbV2z8CHbl80/2hm3XPEG4JgNdQLK81IBRXmSxHfMAOkSqQeRxT/0dwNDz2GOm3zzpcQ==",
       "dev": true,
       "license": "MPL-2.0",
       "engines": {
@@ -5801,6 +5803,19 @@
         "url": "https://github.com/sponsors/jonschlinkert"
       }
     },
+    "node_modules/playwright-core": {
+      "version": "1.64.0",
+      "resolved": "https://registry.npmjs.org/playwright-core/-/playwright-core-1.64.0.tgz",
+      "integrity": "sha512-T9r+MZkTECl2+oUcZ26YgZzTrYidTsIhYYkJix+6iDOymOb1FB2RLLSOxRGnZGv5DStt+aduIVbt+E8WygXYpg==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "playwright-core": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
     "node_modules/possible-typed-array-names": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/possible-typed-array-names/-/possible-typed-array-names-1.1.0.tgz",