fix(distribution): stop release-please dropping stale version in pad.xml URL

Primary_Download_URL held the version twice on one marked line, so
release-please's generic updater (single-replace per line) only bumped
the tag segment and left the installer filename stale, breaking xtask
verify on v1.36.0's release build. Marker comments removed from
pad.xml/config; the existing PAD sync workflow step now sets
Program_Version and Primary_Download_URL atomically from
src-egui/Cargo.toml instead.

Closes #165