web: sim store, URL state scheme, debounced parallel runs (M3 slice 2)

useSimStore is the one reactive module singleton from the spec: panels
over a shared base config, runs debounced 400 ms, one POST /api/scenario
per panel in parallel, results swapped in atomically only when every
request succeeds. Failures keep the last good results; engine 400s are
routed to an inline validationError, everything else to the banner
message. Stale in-flight responses lose to newer runs per panel.

URL state follows spec section 7 (readable params, repeated panel=,
focus index, full fallback to the preset on any malformed part) and is
covered by round-trip and rejection tests. The study copy and initial
panels live in the deepfake-school preset module; formatPct is the
single percent-rounding rule.

The vitest tsconfig now keeps lib at ES2022 like the app config, and
prettier skips the tygo-generated src/types (drift guard stays green).

web/tsconfig.vitest.json

@@ -8,8 +8,10 @@
 
   "compilerOptions": {
     // Vitest runs in a different environment than the application code.
-    // Adjust lib and types accordingly.
-    "lib": [],
+    // Adjust lib and types accordingly. The language lib stays ES2022 (as in
+    // the app config) so app code imported by tests type-checks the same;
+    // only the DOM globals come from jsdom instead.
+    "lib": ["ES2022"],
     "types": ["node", "jsdom"],
 
     // `vue-tsc --build` produces a .tsbuildinfo file for incremental type-checking.