feat(scope): dsh-scope scoped-context registration primitive

createScope(ctx, key) mints a tagged context over a synchronously-usable
no-op-plugin fiber (one fact drives visibility AND lifetime); scopeOf reads
the tag through the prototype chain; scopeTarget(base, key) builds the
scope-filtered dispatch carrier over cordis Context.filter, composing the
base's own filter, branded Scoped<T> and runtime-marked for the dev
invariants. Scope.rawDispose exposes the exact cordis disposer so a
composite effect can nest the scope's teardown at its yield position.

tsconfig.json

@@ -24,6 +24,7 @@
     { "path": "./packages/util/brand" },
     { "path": "./packages/llm/llm" },
     { "path": "./packages/core/session" },
+    { "path": "./packages/core/scope" },
     { "path": "./packages/session-persistence/session-persistence" },
     { "path": "./packages/session-persistence/session-persistence-jsonl" },
     { "path": "./packages/session-persistence/session-persistence-sqlite" },