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