capsite/lib: MapStore and patterns work-alikes

Enough of @agoric/store's MapStore and @endo/patterns' M for the
credential-rotation design: makeMapStore(label, { keyShape, valueShape },
kv) keeps entries in a DO's sync KV under store:<label>:, and readOnly()
hands out the queries alone. Facets are workerd RpcTargets in place of
endo's Far.

Unlike endo, error messages never include keys or values: the values
here are credentials, and messages cross RPC into logs.

Generated-by: Claude Opus 5.5

lib/tests/tsconfig.json

@@ -0,0 +1,7 @@
+{
+	"extends": "../tsconfig.json",
+	"compilerOptions": {
+		"types": ["@cloudflare/vitest-plugin/types"]
+	},
+	"include": ["./**/*", "../src/**/*", "../worker-configuration.d.ts"]
+}