v2.10.3: spread nightly maintenance across targets; drop dead files

- Tier now walks one target at a time with a pause between them, and pauses again
  every few file rewrites. Doing all targets in one burst rewrote dozens of day files
  back to back, which on a box also serving charts showed up as a nightly IO spike.
- removed config.example.jsonc (config files were dropped back in v2.1, nothing reads
  it) and five unreferenced hero images; README only uses hero8 and hero9
- clean.sh stays: file storage still benefits from a manual purge tool

Author: githubflyideas