chore(sponsors): drop AICoding partner from README, presets and i18n

Remove AICoding (aicoding.sh) sponsor entry from the three README files
and the provider preset across all seven app_types (claude, codex,
gemini, hermes, opencode, openclaw, claudeDesktop). Also drop the
matching partner_promotion.aicoding string in zh/en/ja locales.

The icon (src/icons/extracted/index.ts) and the legacy provider id in
codex_history_migration.rs are kept intentionally: the former for
possible later re-use, the latter so existing users' Codex history
still gets bucketed into "custom" on upgrade.