docs: range-read M4 (openUrl in the browser): changelog, limits, design status

CHANGELOG (Unreleased), known-issues (the browser can open URLs; the
limits of openUrl: round trips per wave of misses, a call holds what it
reads, CORS and validator visibility, the download fallback), the M4
status in docs/design/range-reads.md (why NeedBytes rather than a
Worker, why not clawhdf5-remote's BlockCache, what was tested; the
status paragraph at the top lost a garbled duplicate), the viewer's
README (API, options, how it works, tests; the size table is marked as
predating openUrl), CLAUDE.md and the README crate list.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

examples/wasm-viewer/test/test.mjs

@@ -247,7 +247,7 @@ async function remoteTests() {
     const server = await serverStats();
     eq(st.requests, server.requests, "big: requests counted");
     eq(st.bytesFetched, server.bytes, "big: bytes counted");
-    console.log(`big.h5 (${big.size} bytes): listed, 3 small reads and a window in ` +
+    console.log(`big.h5 (${big.size} bytes): listed, 2 small reads, attributes, info and a window in ` +
       `${server.requests} requests, ${server.bytes} bytes (${(100 * server.bytes / big.size).toFixed(2)}%)`);
     assert.ok(server.requests <= 8, `big: ${server.requests} requests`);
     assert.ok(server.bytes * 20 < big.size, `big: ${server.bytes} bytes fetched`);