docs: document ACL API, RedisURI auth/config, HyperLogLog & hash field-expiration

[yisraelU]

What

Documentation-only follow-up to the recently merged ACL (#1144) and RedisUriConfig (#1143) work, plus a sweep that closed two adjacent gaps found along the way.

ACL

• New site/docs/effects/acl.md covering the AclCommands algebra: usage, the typed SETUSER rules (AclSetUserRule / AclCategory / RawCommand) with a rule → ACL SETUSER mapping table, the AclUser/AclSelector GETUSER result and its Option/absence semantics, ACL CAT, the ACL log, and AclError (UnknownCommand / DecodingFailure) + the string-codec note.
• Listed in the effects API index.

RedisURI authentication & config

• Reworked the Client page's authentication section to make the URI-config ↔ auth relationship explicit: the three ways to supply credentials, the RedisCredentials sum type (Password vs UsernameAndPassword = ACL user), how RedisUriConfig.withCredentials ties in, sentinel per-node passwords, and connection-time vs runtime (Connection API auth) authentication — cross-linked to the ACL page.

Other gaps closed

• New site/docs/effects/hyperloglog.md (PFADD/PFCOUNT/PFMERGE) + index entry — the algebra previously had no page.
• Documented the Redis 7.4+ per-field expiration and read-and-modify hash commands in hashes.md: hExpire/hExpireAt (+ ExpireExistenceArg), httl/hpttl, hExpireTime/hpExpireTime, hPersist, hGetEx (HGetExArgs) and hGetDel.

Verification

• sbt microsite/mdoc — 0 errors; all new scala mdoc blocks type-check against the effects module.
• Remaining mdoc warnings are the repo's pre-existing .html-link / unused-binder style warnings, uniform with every existing doc.

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