compat(redis): make TIME-using Lua scripts work on Redis 3.2-4.x

[ghostg00]

Summary

Eight Lua scripts in backend/internal/repository/ call redis.call('TIME') to read the Redis server clock — by design, to avoid client-side clock skew across multiple application instances (the existing inline comments document this rationale).

TIME is non-deterministic, and Redis replicates that to replicas / AOF differently across versions. This PR adds a single redis.replicate_commands() call at the top of each affected script so the resulting writes (ZADD, ZREMRANGEBYSCORE, SET, DEL, EXPIRE) replicate correctly on Redis 3.2 – 4.x.

Compatibility

Redis version	Behavior of redis.replicate_commands()	Effect of this PR
3.2 – 4.x	Required — switches Lua from script replication to effects replication so non-deterministic command effects can be propagated	Fixes incorrect replication / silent divergence on replicas and AOF
5.0 – 6.x	No-op — effects replication is the default	No-op — behavior unchanged
7.0+	Still callable, marked deprecated (not removed); the docs still list it as the supported way to opt into effects replication when needed	No-op — behavior unchanged

The bundled deploy/docker-compose*.yml files pin redis:8-alpine, so this never surfaces on the default stack. It only surfaces in deployments running against older Redis instances (private/enterprise registries, on-prem setups), which is where this fix is needed.

Why not pass the timestamp in via ARGV?

Each affected script's inline comment explicitly documents the design intent: read the time from the Redis server so the timestamp source stays consistent across multiple application instances. Switching to a client-supplied ARGV timestamp would regress that design and reintroduce the clock-skew problem this code was written to avoid. Opting into explicit command replication is the correct fix.

Affected scripts (8 total)

File	Scripts
backend/internal/repository/concurrency_cache.go	acquireScript, getCountScript, cleanupExpiredSlotsScript
backend/internal/repository/session_limit_cache.go	registerSessionScript, refreshSessionScript, getActiveSessionCountScript, isSessionActiveScript
backend/internal/repository/user_msg_queue_cache.go	releaseLockScript

Scripts that do not invoke non-deterministic commands (incrementWaitScript, decrementWaitScript, acquireLockScript, forceReleaseLockScript, startupCleanupScript, …) are intentionally left untouched.

Test plan

• go build ./... passes
• Existing repository tests pass against redis:8-alpine (no behavior change, since redis.replicate_commands() is a no-op there)
• Manual smoke test against a Redis 4.x primary + replica setup, verifying the affected scripts execute and replicate cleanly

Diff size

3 files changed, 24 insertions(+) — two comment lines + one call per script.

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[ghostg00]

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