chore(deps): add eslint-plugin-boundaries to apps/app

Adds eslint-plugin-boundaries@6.0.2 (MIT, peerDeps eslint>=6,
engines node>=18.18) as a direct devDep in apps/app/package.json,
matching the exact-pin style of the other 14 eslint-plugin-* deps.

Direct dep — not hoisted transitive — per the
TECH-PORTAL-ESLINT-DEPS lesson (Cursor's ESLint extension uses
strict module resolution and silently fails on plugins reachable
only via pnpm hoisting).

Plugin not yet enabled in .eslintrc.cjs; enabling lands in the next
commit per WS-3 1c sequence (audit Phase A → install → enable →
refactor axios.ts → docs).

Tests + typecheck verified green post-install.

Co-Authored-By: Claude <noreply@anthropic.com>

apps/app/package.json

@@ -106,6 +106,7 @@
     "eslint-config-airbnb-base": "15.0.0",
     "eslint-import-resolver-typescript": "3.10.1",
     "eslint-plugin-antfu": "0.43.1",
+    "eslint-plugin-boundaries": "6.0.2",
     "eslint-plugin-case-police": "0.6.1",
     "eslint-plugin-es-x": "7.8.0",
     "eslint-plugin-eslint-comments": "3.2.0",