release(v4.0.2): consumer-strict reader-shape fixes

4.0.1's typecheck gate compiled each package internally against
lib: ["ES2022"]. That doesn't catch types that only fail when
*consumer* code (lib: ["DOM"] + exactOptionalPropertyTypes) tries to
assign a native browser type into one of our locally-defined narrower
types. Dispatch hit one such case in @shade/files inline-threshold.ts.

This release adds a tests/consumer-strict/ smoke project to the
pre-publish gate. It compiles a tiny "as if I were a downstream app"
TS file against:

  lib: ["ES2022", "DOM", "DOM.Iterable"]
  types: ["bun-types"]
  exactOptionalPropertyTypes: true
  strict: true
  paths → packages/*/src/index.ts

scripts/typecheck-all.ts now runs the smoke after per-package checks.
Both must pass before publish:dry / publish:all proceeds.

### Fixed
- @shade/files inline-threshold.ts: MinimalReader<T> rewritten as the
  explicit disjoint union { done:false, value:T } | { done:true,
  value?: T | undefined } that's assignable from every native reader
  shape (bun, DOM, node:stream/web). Fixes the
  "ReadableStreamReadResult is not assignable" Dispatch reported.
- @shade/files streams-bridge (client + server): stash setTimeout
  return in a local before .unref?.() via { unref?: () => void } cast.
  Fluent .unref?.() failed under lib: ["DOM"] (setTimeout returns
  number there).
- @shade/sdk background.ts: same setInterval .unref?.() fix.

Wire-compatible. No API shape changed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/consumer-strict/use-key-transparency.ts

@@ -0,0 +1,42 @@
+/**
+ * Consumer-strict smoke for `@shade/key-transparency`.
+ *
+ * The package was the source of the 4 noUnusedLocals + the IndexProofWire
+ * privacy bug in 4.0.0. This smoke imports every public type and
+ * exercises the witness-fetcher contract that the SDK plugs into.
+ */
+import {
+  LightWitness,
+  type SignedTreeHead,
+  type STHWire,
+  type WitnessFetcher,
+} from '@shade/key-transparency';
+
+declare const crypto: import('@shade/core').CryptoProvider;
+declare const logPublicKey: Uint8Array;
+
+async function smoke(): Promise<void> {
+  const fetcher: WitnessFetcher = {
+    async fetchLatestSTH(): Promise<STHWire> {
+      const res = await fetch('https://shade.example.com/v1/kt/sth');
+      return (await res.json()) as STHWire;
+    },
+    async fetchConsistencyProof(
+      from: number,
+      to: number,
+    ): Promise<{ proof: string[] }> {
+      const res = await fetch(
+        `https://shade.example.com/v1/kt/consistency?from=${from}&to=${to}`,
+      );
+      return (await res.json()) as { proof: string[] };
+    },
+  };
+  const witness = new LightWitness({ crypto, logPublicKey, fetcher });
+  void witness;
+}
+
+void smoke;
+
+// Verify the type is reachable with no `any` leak.
+declare const sth: SignedTreeHead;
+void sth.treeSize;