feat: Configure Redis memory limits for low-memory devices

[mverteuil]

Summary

Reduces Redis memory limit from 256MB to 64MB and ensures the optimized Redis configuration is deployed during installation.

Problem

On a Raspberry Pi 3B with 417MB RAM:

• Redis had no memory limit (maxmemory: 0B)
• System was using 199M/200M swap (nearly full)
• Python daemons were consuming ~167MB combined
• Risk of swap thrashing and poor performance

Current Memory Usage (before fix)

               total        used        free      shared  buff/cache   available
Mem:           417Mi       234Mi       106Mi        16Ki       125Mi       182Mi
Swap:          199Mi       2.0Mi       197Mi

Top processes:

• update-daemon: 51MB (12%)
• epaper-display-daemon: 41MB (9.7%)
• audio-websocket-daemon: 32MB (7.6%)
• uvicorn: 14MB (3.5%)
• audio-capture: 14MB (3.4%)
• audio-analysis: 14MB (3.3%)

Solution

1. Reduced Redis memory limit from 256MB → 64MB in config_templates/redis.conf
2. Added configure_redis() function to deploy the configuration during installation
3. Updated installer to run Redis configuration in Wave 4 (parallel with Caddy config)

Memory Allocation Strategy

For devices with 512MB RAM or less:

• Redis: 64MB (hard capped with LRU eviction)
• Python daemons: ~167MB
• System: ~70MB
• Available: ~116MB
• Swap: minimal usage

Configuration Changes

• maxmemory 64mb - Hard limit prevents Redis from consuming excess memory
• maxmemory-policy allkeys-lru - Evict least-recently-used keys when limit reached
• Persistence disabled (memory-only mode to protect SD card)

Benefits

• Prevents swap thrashing on low-memory SBCs
• Predictable memory usage for Redis
• More memory available for Python daemons
• Better overall system responsiveness
• Automatic deployment via installer

Testing

After installation, verify with:

redis-cli INFO memory | grep maxmemory_human

Should show: maxmemory_human:64.00M