feat(reality): derive a stable per-client spiderX for shared links

The inbound's spiderX now acts as a per-client seed: exports emit
sha256(seed|subKey) truncated to a 15-hex "/path", so a client's spx no
longer changes on every subscription fetch (#5718) while different
clients stop sharing one fingerprintable value. The form gains a
regenerate button that rotates every client's path at once.

The frontend link builders derive through the same function
(lib/xray/spider-x.ts, @noble/hashes) keyed on subId-then-email like
the Go subKey, so panel QR/copy links and subscription output agree —
cross-language vector tests lock both sides byte-for-byte. streamData
now tolerates malformed stored stream settings (unparseable JSON, null
tls/reality settings) instead of panicking the subscription request.

frontend/src/test/inbound-form-blocks.test.tsx

@@ -104,6 +104,7 @@ describe('inbound security forms', () => {
         scanRealityCandidates={async () => []}
         applyRealityScanResult={noop}
         randomizeShortIds={noop}
+        randomizeSpiderX={noop}
         genRealityKeypair={noop}
         clearRealityKeypair={noop}
         genMldsa65={noop}