Remove webclient (extracted to Webatrice repo) (#6848)

The webclient has been extracted to https://github.com/seavor/Webatrice
and the Playwright e2e suite has moved to Sockatrice. Cockatrice keeps
no copy.

Deleted:
- webclient/ (entire tree, 349 files)
- .github/workflows/web-build.yml, web-lint.yml
- .husky/pre-commit (the only tracked husky hook; managed entirely
  from webclient's package.json which no longer exists)

Edited:
- .tx/config: dropped the webclient resource block; Webatrice/.tx/config
  now manages its own translations
- .github/workflows/translations-pull.yml: removed webclient locales
  from add-paths
- .github/workflows/desktop-build.yml, desktop-lint.yml: removed dead
  '!webclient/**' and '!.husky/**' path-filter exclusions
- .github/dependabot.yml: removed commented-out npm/webclient block
- Doxyfile: removed webclient/ from EXCLUDE list
- .ci/release_template.md: dropped Webatrice section (Webatrice now
  cuts its own releases)
- README.md: dropped 'first work on a webclient' line, added Webatrice
  to Related Repositories, updated translation paragraph and build
  badges

History preserved: every webclient commit remains recoverable via
git log on master before this commit.

webclient/package.json

@@ -1,94 +0,0 @@
-{
-  "name": "webclient",
-  "version": "1.0.0",
-  "private": true,
-  "scripts": {
-    "prebuild": "node prebuild.js",
-    "prestart": "node prebuild.js",
-    "build": "react-scripts build",
-    "start": "react-scripts start",
-    "test": "react-scripts test",
-    "test:watch": "react-scripts test",
-    "eject": "react-scripts eject",
-    "lint": "eslint \"./**/*.{ts,tsx}\"",
-    "lint:fix": "eslint \"./**/*.{ts,tsx}\" --fix",
-    "golden": "npm run lint && npm run test",
-    "prepare": "cd .. && husky install",
-    "translate": "node prebuild.js -i18nOnly"
-  },
-  "dependencies": {
-    "@emotion/react": "^11.8.2",
-    "@emotion/styled": "^11.8.1",
-    "@mui/icons-material": "^5.5.1",
-    "@mui/material": "^5.5.1",
-    "crypto-js": "^4.2.0",
-    "dexie": "^3.2.2",
-    "final-form": "^4.20.6",
-    "final-form-set-field-touched": "^1.0.1",
-    "i18next": "^22.0.4",
-    "i18next-browser-languagedetector": "^7.0.0",
-    "i18next-icu": "^2.0.3",
-    "intl-messageformat": "^10.2.1",
-    "lodash": "^4.17.21",
-    "prop-types": "^15.8.1",
-    "protobufjs": "^7.2.4",
-    "react": "^18.2.0",
-    "react-dom": "^18.2.0",
-    "react-final-form": "^6.5.8",
-    "react-final-form-listeners": "^1.0.3",
-    "react-i18next": "^12.0.0",
-    "react-redux": "^8.0.4",
-    "react-router-dom": "^6.2.2",
-    "react-scripts": "5.0.1",
-    "react-virtualized-auto-sizer": "^1.0.6",
-    "react-window": "^1.8.6",
-    "redux": "^4.1.2",
-    "redux-form": "^8.3.8",
-    "redux-thunk": "^2.4.1",
-    "rxjs": "^7.5.4",
-    "sanitize-html": "^2.7.3"
-  },
-  "devDependencies": {
-    "@babel/core": "^7.17.5",
-    "@mui/types": "^7.1.3",
-    "@testing-library/jest-dom": "^5.16.2",
-    "@testing-library/react": "^13.4.0",
-    "@types/jest": "29.2.0",
-    "@types/jquery": "^3.5.14",
-    "@types/lodash": "^4.14.179",
-    "@types/node": "18.11.7",
-    "@types/prop-types": "^15.7.4",
-    "@types/react": "18.0.24",
-    "@types/react-dom": "18.0.8",
-    "@types/react-redux": "^7.1.23",
-    "@types/react-router-dom": "^5.3.3",
-    "@types/react-virtualized-auto-sizer": "^1.0.1",
-    "@types/react-window": "^1.8.5",
-    "@types/redux-form": "^8.3.3",
-    "@typescript-eslint/eslint-plugin": "^5.14.0",
-    "@typescript-eslint/parser": "^5.14.0",
-    "fs-extra": "^10.0.1",
-    "husky": "^8.0.1",
-    "typescript": "^4.6.2"
-  },
-  "eslintConfig": {
-    "extends": "react-app"
-  },
-  "browserslist": {
-    "production": [
-      ">0.2%",
-      "not dead",
-      "not op_mini all"
-    ],
-    "development": [
-      "last 1 chrome version",
-      "last 1 firefox version",
-      "last 1 safari version"
-    ]
-  },
-  "jest": {
-    "moduleNameMapper": {
-      "\\.(css|less)$": "identity-obj-proxy"
-    }
-  }
-}