contacts: fix lousiana->louisiana, relocate mayorial photo-directives, additively backfill mayors

Cleanup:
- Rename senatorial/state/lousiana.filtered.emails.txt -> louisiana.filtered.emails.txt
- Rename mayorial/state/lousiana -> mayorial/state/louisiana
- Move mayorial/state/photo-directives -> mayorial/photo-directives (image
  assets are not a state; out of the per-state list)

Mayorial backfill (additive only):
- Merge municipal MAYOR-role emails from the public openstates/people dataset
  into each state, appending only addresses not already present. No existing
  address was removed or overwritten; richer curated lists (CA, FL, TX, ...)
  are preserved intact.
- 477 net-new mayor emails added; 17 states that had no file were created.
  Mayorial now covers 50 states.
- Add contacts/mayorial/README.md documenting layout, sources, and coverage
  limits (US Conference of Mayors data is paid; get.gov email is a DNS/security
  contact, not the mayor; OpenStates municipal coverage is partial).

Author: kiro-agent