chore(tooling): add eslint + prettier, fix the test watch-mode default

Three gaps in the frontend tooling, all in the package.json script surface.

1. No JS/TS linter or formatter existed at all for 274 TS/Svelte files.

   Adds an ESLint flat config (typescript-eslint + eslint-plugin-svelte,
   Svelte 5 + TS strict) and prettier + prettier-plugin-svelte, plus the
   `lint`, `lint:fix`, `format`, `format:check` scripts.

   The tree is error-clean (`npx eslint .` exits 0). Getting there needed
   seven real one-line fixes (braced switch cases that leaked `const` across
   arms, a useless regex escape, two `let`s that never change, a thrown Error
   that dropped its `cause`, and two `// eslint-disable-next-line` comments
   documenting the Svelte 5 bare-read-for-dependency idiom). Everything else
   that fires is set to `warn` with the reason written next to it in
   eslint.config.js — notably ~94 dead bindings and `any` at the IPC
   boundary. Those are real findings to drive to zero, not noise to delete.

   `no-console` is OFF for now: a parallel change is moving all ~468 console
   calls onto a logger facade, and turning the rule on today would collide
   with it. eslint.config.js says so, and says to flip it to `error` once
   that lands.

   `prettier --write` is deliberately NOT run here — it would rewrite ~200
   files and swamp every other diff in flight. The gate is available; the
   sweep is a separate commit. Markdown and CI YAML are in .prettierignore
   because both are hand-laid-out (and docs/traceability.md is generated).

2. `bun run test` was bare `vitest`, i.e. watch mode — while CLAUDE.md's
   "Before Committing" list tells people to run it. It is now `vitest run`,
   with `test:watch` and `test:coverage` (also `--run`-ified) alongside.
   scripts/test-all.sh drops the now-redundant `--run`, and
   scripts/test-frontend.sh keeps `--watch`/`--ui`/`-w` working by routing
   them to a long-running vitest instead of the single-pass one.

3. The webdriverio e2e suite is deleted. It was last touched in January
   ("First working POC"), has never run since, and is not in CI — five
   devDependencies and two scripts of pure decoration. Removes e2e/,
   wdio.conf.ts, the two `test:e2e*` scripts, the @wdio/* + webdriverio
   devDeps, and the WebdriverIO block in .gitignore.

The package.json diff also carries `hooks:install` and `check:links`, wired
up by the following commits.

package.json

@@ -10,14 +10,19 @@
     "preview": "vite preview",
     "check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
     "check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
-    "test": "vitest",
+    "test": "vitest run",
+    "test:watch": "vitest",
     "test:ui": "vitest --ui",
-    "test:coverage": "vitest --coverage",
-    "test:e2e": "wdio run ./wdio.conf.ts",
-    "test:e2e:dev": "wdio run ./wdio.conf.ts --watch",
+    "test:coverage": "vitest run --coverage",
     "test:all": "./scripts/test-all.sh",
     "test:rust": "./scripts/test-rust.sh",
+    "lint": "eslint .",
+    "lint:fix": "eslint . --fix",
+    "format": "prettier --write .",
+    "format:check": "prettier --check .",
     "check:boundary": "bash scripts/check-frontend-boundary.sh",
+    "check:links": "bash scripts/check-doc-links.sh",
+    "hooks:install": "./scripts/install-hooks.sh",
     "android:build": "./scripts/build-android.sh",
     "android:build:release": "./scripts/build-android.sh release",
     "android:build:device": "./scripts/build-android.sh --device",
@@ -51,6 +56,7 @@
     "svelte-dnd-action": "^0.9.69"
   },
   "devDependencies": {
+    "@eslint/js": "^10.0.1",
     "@sveltejs/adapter-static": "^3.0.6",
     "@sveltejs/kit": "^2.9.0",
     "@sveltejs/vite-plugin-svelte": "^6.2.4",
@@ -59,18 +65,20 @@
     "@testing-library/svelte": "^5.3.1",
     "@vitest/coverage-v8": "^4.0.18",
     "@vitest/ui": "^4.0.16",
-    "@wdio/cli": "^9.5.0",
-    "@wdio/local-runner": "^9.5.0",
-    "@wdio/mocha-framework": "^9.5.0",
-    "@wdio/spec-reporter": "^9.5.0",
+    "eslint": "^10.8.1",
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-svelte": "^3.23.0",
+    "globals": "^17.11.0",
     "happy-dom": "^20.0.11",
     "jsdom": "^27.4.0",
+    "prettier": "^3.9.6",
+    "prettier-plugin-svelte": "^4.1.1",
     "svelte": "^5.47.1",
     "svelte-check": "^4.0.0",
     "tailwindcss": "^4.1.18",
     "typescript": "~5.6.2",
+    "typescript-eslint": "^8.67.0",
     "vite": "^6.0.3",
-    "vitest": ">=1.0.0 <5.0.0",
-    "webdriverio": "^9.5.0"
+    "vitest": ">=1.0.0 <5.0.0"
   }
 }