fix(shell): the shell's typecheck has never passed — missing css shim and a wrong element type

`pnpm --filter @augment-it/shell check` failed with two errors, and had done
since the check script was written. Both are now fixed and the shell typechecks
clean for the first time.

The missing CSS shim had a root cause worth naming. shell/src/index.ts does a
side-effect import of '@augment-it/theme/theme.css', which carries no type
declarations — rsbuild resolves it at build time, but svelte-check cannot.
Every app under apps/ ships a src/css.d.ts declaring `*.css` ambiently. The
shell never did, and adding one would not have helped: shell/tsconfig.json was
a byte-identical copy of the apps' old drifted variant, and that variant omits
"src/**/*.d.ts" from `include`, so the shim would have been ignored. Both
halves are fixed together — the shim exists, and the shell now extends
tsconfig.base.json like the apps do.

That makes the shell the eighteenth copy of the config converged earlier today,
found only because this bug pointed at it. Its tsconfig drops from 20 lines to
4.

The second error was a real type mismatch rather than a config artifact.
`stageEl` was declared HTMLDivElement but is bound to `<main class="stage">`,
which is an HTMLElement. Widened to HTMLElement, which is safe: the only member
ever called on it is getBoundingClientRect(). Annotation-only — no runtime
change, and the built output is unaffected.

Verified: shell 93 files clean, and 1,587 files across all seventeen apps plus
the shell now check with zero errors, up from 1,494 with the shell failing
outright. 19 packages build.

Files changed:
- shell/src/css.d.ts (new)
- shell/tsconfig.json
- shell/src/App.svelte
- tsconfig.base.json

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019a8tSPbFdvF1pKtADnWyDg

Author: mpstaton

shell/src/App.svelte

@@ -196,7 +196,9 @@
 
   // ---- transient interaction state (never persisted) ----------------------
   let hoveredNeighborId = $state<string | null>(null);
-  let stageEl = $state<HTMLDivElement | undefined>(undefined);
+  // HTMLElement, not HTMLDivElement — this binds to <main class="stage">, and
+  // only getBoundingClientRect() is ever called on it.
+  let stageEl = $state<HTMLElement | undefined>(undefined);
   let resizing = $state<boolean>(false);
   let splitting = $state<boolean>(false);
 

shell/src/css.d.ts

@@ -0,0 +1,9 @@
+// Side-effect CSS imports (@augment-it/theme/theme.css) carry no type
+// declarations — rsbuild resolves them at build time. Declare them ambiently
+// so svelte-check / tsc (stricter under TS 6) can resolve the side-effect
+// imports instead of erroring on the missing module.
+//
+// Every app under apps/ has carried this shim; the shell never did, because
+// its tsconfig omitted "src/**/*.d.ts" from `include` and the file would have
+// been ignored anyway. Both halves are fixed together.
+declare module '*.css';

shell/tsconfig.json

@@ -1,21 +1,5 @@
 {
-  "compilerOptions": {
-    "target": "ES2022",
-    "module": "ESNext",
-    "moduleResolution": "bundler",
-    "lib": ["DOM", "DOM.Iterable", "ES2022"],
-    "strict": true,
-    "noImplicitAny": true,
-    "esModuleInterop": true,
-    "skipLibCheck": true,
-    "resolveJsonModule": true,
-    "verbatimModuleSyntax": true,
-    "noEmit": true,
-    "allowImportingTsExtensions": true,
-    "isolatedModules": true,
-    "useDefineForClassFields": true,
-    "types": ["svelte"]
-  },
-  "include": ["src/**/*.ts", "src/**/*.svelte", "src/**/*.svelte.ts"],
+  "extends": "../tsconfig.base.json",
+  "include": ["src/**/*.ts", "src/**/*.svelte", "src/**/*.svelte.ts", "src/**/*.d.ts"],
   "exclude": ["node_modules", "dist"]
 }

tsconfig.base.json

@@ -1,6 +1,7 @@
 {
   "_comment": [
-    "Shared TypeScript config for every federated member under apps/.",
+    "Shared TypeScript config for every federated member under apps/, plus the",
+    "federation host in shell/.",
     "Before this file the 17 apps carried three byte-distinct tsconfig.json",
     "variants in an 8/7/2 split \u2014 drift, not intent. The two differences were",
     "an extra 'src/**/*.d.ts' include (kept, it picks up css.d.ts) and a",