build(source-os): make installed sourceos-office path-safe

[mdheller]

Summary

Fix the installed sourceos-office front door so it resolves sibling helpers first and only falls back to repo-relative helpers when run from the repo tree.

Files:

• build/office-suite/scripts/sourceos-office
• build/office-suite/scripts/install_sourceos_office_shell_smoke.sh

Why

Current main stages sourceos-office into ~/.local/bin, but the script still computes ROOT repo-relatively. That works in-repo and breaks when installed. This follow-on closes that installed-path bug and proves it with the shell smoke.

[mdheller]

Agent triage: closing this PR as superseded by current main.

main already includes the installed-path-safe sourceos-office helper and a stronger install_sourceos_office_shell_smoke.sh that covers the installed command, verify path, search path, and new-document path. This branch is also 64 commits behind main, so merging it would be redundant and risky.