docs/execution-model.md subcommand list is severely outdated

[codeforester]

Problem

docs/execution-model.md lists the current Base subcommands under "Umbrella Base Command":

- setup
- check
- clean
- doctor
- activate
- test
- run
- projects list
- update-profile
- version
- help

This list is missing eight implemented subcommands:

• demo (shipped — manifest-declared demo runner)
• repo (shipped — repo init/check/configure)
• logs (shipped — log listing and tailing)
• workspace (shipped — status/check/doctor)
• onboard (shipped — guided first-run flow)
• gh (shipped — GitHub workflow helpers)
• config (shipped — user config inspection)
• update (shipped — repo update and re-setup)

The execution model document is the canonical reference for how basectl dispatches commands. A contributor reading this page gets a materially wrong picture of what Base does.

Fix

Update the subcommand list to include all shipped commands. Add a note that the canonical list is always basectl --help, and link to the help output or the help text in basectl.sh rather than maintaining a duplicate list in prose.