fix(decrypt): bump hashtag+subscription decrypt timeout 6s->15s; document lists-decrypt root cause

Real-env console shows the encrypted lists are FETCHED but DECRYPTION fails on
cold login: hashtags time out at 6s, blocks report signerStatus 'missing', DMs
throw 'helpers unavailable'. Root cause: a relay-connection storm to the user's
~20 dead NIP-65 relays (subsystems use uncapped relayManager read+write) starves
the nip-07 extension. Bumping the decrypt timeout to 15s (matching blocks) is a
partial mitigation for hashtags/subscriptions. The proper fix (bound reads to a
liveness-ranked healthy core incl. defaults + DM decrypt retry) is documented in
KNOWN_BUGS #0 — a first capReadRelays attempt was reverted because capping block
reads broke the security-critical user-blocks integration test.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/subscriptions.js

@@ -53,7 +53,7 @@ const SUBSCRIPTION_SET_KIND =
 // so decryption should succeed within 2-3s. 6s is generous enough for slow
 // relays while still failing fast enough for the scheme fallback to try the
 // next decryption method without stalling the login path.
-const DECRYPT_TIMEOUT_MS = 6000;
+const DECRYPT_TIMEOUT_MS = 15000;
 // PERF: Reduced from 3s to 1.5s — extensions that already granted permission
 // should recover near-instantly. The shorter delay prevents unnecessary wait
 // time during the critical login path when the first decrypt attempt fails.