fix(build): stop the host tree leaking into the image, split the tsc lanes

Review round 1 fallout, all of it verified against real builds:

- .dockerignore: `node_modules/` is anchored at the context root and has no
  implicit `**/` (unlike gitignore), so it never matched frontend/node_modules.
  `COPY frontend/ ./` was overlaying the Windows host's node_modules on top of
  what `npm ci` had installed — the image carried @esbuild/win32-x64 and 31 .cmd
  shims, and the new typecheck ran a tsc resolved from that merged tree. Build
  context transfer drops 3.05 GB -> 19 kB. Also excludes e2e/.auth (a live
  Playwright session), the report/result dirs and logs.
- build no longer type-checks the e2e project: a type error in a spec must not
  make the app unbuildable for a self-hoster. The gate still checks it via
  `npm run typecheck` (now three named lanes).
- tsconfig.json references tsconfig.node.json, so editors check vite.config.ts /
  vitest.config.ts under the same config the gate uses instead of an inferred one.
- vitest include accepts .test.tsx: an uncollected test file does not fail, it
  silently never runs.

frontend/tsconfig.json

@@ -15,5 +15,10 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true
   },
-  "include": ["src"]
+  "include": ["src"],
+  // Editors resolve a file to the nearest tsconfig that INCLUDES it; vite.config.ts / vitest.config.ts
+  // are in neither this project's `include` nor e2e's, so without this reference the language service
+  // falls back to an inferred project (non-strict, DOM lib) and shows you different errors than
+  // `npm run typecheck` does. The reference makes the editor and the gate agree.
+  "references": [{ "path": "./tsconfig.node.json" }]
 }