Fix InfluxDB data directory permission issue after install (#88)

[y-vectorfield]

Description

Fixes #88

Problem

On Ubuntu 24.04 fresh installs, pironman5 service can be active, but data logging fails due to InfluxDB shard file permission denied errors under /var/lib/influxdb/data.

Cause

InfluxDB data directory ownership and modes are not normalized during installation in this flow, which can leave runtime write permissions inconsistent.

Changes

• Add post-install permission normalization for /var/lib/influxdb
• Set ownership to influxdb:influxdb when the directory exists
• Normalize directory permissions to 755
• Normalize file permissions to 644

Why this is safe

• Runs only when /var/lib/influxdb exists
• Uses standard InfluxDB ownership and conservative filesystem modes
• Does not change service startup logic or unrelated installer behavior

Testing

Verified on Ubuntu 24.04.4 LTS:

• pironman5 service reaches active running state
• Repeated InfluxDB permission denied shard errors no longer appear
• Data logger starts normally after service restart

[y-vectorfield]

@cavonlee , please review my PR. If there are not any problems, please approve and merge my modifications.

[y-vectorfield]

@kyuuinochi , please review my PR. If there are not any problems, please approve and merge my modifications.