feat(web): state the rules, reach the chat from the top of the board, lint the tree

A /rules page says, in one place, what nothing in the app said before:
the chain rule, the clock, what a dead end costs, elimination and the last
player standing, how a word is scored and the reconnect window. Linked
from the landing page and from the board and lobby headers.

The chat control moves above the chain as a pill with the unread count,
where it can be reached on a phone mid-game, and the lobby's folded chat
now carries an unread badge too.

ESLint with the Svelte and JSDoc plugins, run in CI; the real findings
it turned up (missing each keys, untyped timer handles) are fixed.

web/package.json

@@ -8,6 +8,7 @@
     "build": "vite build",
     "prepare": "svelte-kit sync",
     "check": "svelte-kit sync && svelte-check --tsconfig ./jsconfig.json",
+    "lint": "eslint .",
     "test": "vite build && vitest run",
     "test:e2e": "vite build && playwright test"
   },
@@ -16,15 +17,23 @@
   },
   "devDependencies": {
     "@bufbuild/protoc-gen-es": "^2.14.1",
+    "@eslint/js": "^10.0.1",
     "@playwright/test": "^1.63.0",
     "@sveltejs/adapter-static": "^3.0.10",
     "@sveltejs/kit": "^2.70.3",
     "@sveltejs/vite-plugin-svelte": "^6.2.4",
     "@types/node": "^26.4.1",
+    "eslint": "^10.11.0",
+    "eslint-plugin-jsdoc": "^64.5.4",
+    "eslint-plugin-svelte": "^3.23.0",
+    "globals": "^17.12.0",
     "jsdom": "^27.4.0",
     "svelte": "^5.57.0",
     "svelte-check": "^4.7.6",
     "vite": "^7.3.6",
     "vitest": "^3.2.4"
+  },
+  "allowScripts": {
+    "esbuild@0.28.2": true
   }
 }