fix: make try init re-source safe through the shell wrapper

[rohaquinlop]

What

Route try exec init to the init logic so re-running try init from a sourced shell re-emits the wrapper instead of opening the interactive selector.

Why

The shell wrapper generated by try init shadows the try binary. When a shell config is sourced again (source ~/.zshrc), the try init line now resolves to the wrapper, which calls try exec — and exec had no init case, falling through to the interactive selector with init <path> as the search query.

Changes

• try.rb: dispatch init in the exec subcommand path, mirroring plain try init behavior.
• spec/tests/test_36_shell_eval.sh: regression tests for bash and zsh asserting try exec init PATH re-emits the wrapper with the new path.
• spec/init_spec.md: document re-sourcing safety.

Note: #105 (zzzhizhia) covers the same exec init dispatch and has been open since March 2026. This PR is an independent implementation with additional bash/zsh regression coverage in test_36_shell_eval.sh and init_spec.md documentation. Happy to close this one if #105 is preferred.