fix(docs): replace unsafe 'bunx omo install' with 'bunx oh-my-openagent install'

Temporarily replaces all 'bunx omo install' references with 'bunx
oh-my-openagent install' to eliminate the supply chain risk where 'bunx
omo' resolves to an unrelated npm package (omo@2.0.0 by fishead).

This is a stopgap. The 'omo' bin alias remains in package.json for
backward compat and Codex marketplace identity (omo@sisyphuslabs), but
docs no longer recommend it as a primary invocation. A longer-term fix
(either claiming the npm name, removing the alias, or namespacing it)
is needed.

Closes #4657