…paths

Add SetCacheDir, SetConfigDir, and SetDataDir to the paths package,
allowing callers to override the default ~/.config/cagent and ~/.cagent
directories at runtime. The getters check for an override (protected by
a RWMutex) before falling back to the platform-specific defaults.

Two new persistent flags are wired in the root command:
  --config-dir  overrides ~/.config/cagent
  --data-dir    overrides ~/.cagent

These are applied in PersistentPreRunE before logging and telemetry
initialization so all downstream consumers honour the overrides. This
is useful when running cagent inside a sandbox where the home directory
is not writable or mapped to a non-standard location.

Assisted-By: cagent