Update deployment validation plan to reflect Phase 1b completion — pjsua2
built from pjproject 2.17 on caliban without sudo. Document the non-obvious
RPATH/patchelf step, the status() method name correction, and two remaining
caveats (not captured by pip install, Docker still runs stub media).
Update README to point at the new docs/pjsua2-build.md and clarify stub-mode
behavior.
