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/spider-x.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest';
+
+import { deriveSpiderX } from '@/lib/xray/spider-x';
+
+// Cross-language vectors shared with TestDeriveSpiderXMatchesFrontendVectors
+// in internal/sub/service_sharelink_test.go: subscription links come from Go,
+// panel links from this module, and the two must agree byte-for-byte.
+describe('deriveSpiderX', () => {
+  it('matches the Go deriveSpiderX vectors', () => {
+    expect(deriveSpiderX('/seed', 'subAlice')).toBe('/c252fbc3ecd3e3c');
+    expect(deriveSpiderX('/', '')).toBe('/d08ed99bd9afc60');
+  });
+
+  it('is stable per client, distinct across clients, and rotates with the seed', () => {
+    expect(deriveSpiderX('/seed', 'subAlice')).toBe(deriveSpiderX('/seed', 'subAlice'));
+    expect(deriveSpiderX('/seed', 'subAlice')).not.toBe(deriveSpiderX('/seed', 'subBob'));
+    expect(deriveSpiderX('/seedA', 'subAlice')).not.toBe(deriveSpiderX('/seedB', 'subAlice'));
+  });
+
+  it('returns empty when there is nothing to derive from', () => {
+    expect(deriveSpiderX('', '')).toBe('');
+  });
+
+  it('emits a /-prefixed 15-hex-char path', () => {
+    expect(deriveSpiderX('/some-seed', 'client@example.com')).toMatch(/^\/[0-9a-f]{15}$/);
+  });
+});