Mark all four IUV-02 subtasks as done in docs/TASKS.md, update
MISSION-MANIFEST milestone table and progress (2/3), and append
Session 3 to the install-ux-v2 scratchpad covering the M02 delivery:
PR #444 merged, CORS→FQDN prompt rework, skill installer selection→
install gap fixed with MOSAIC_INSTALL_SKILLS whitelist, 18 new tests.
Refs #437
