Adding CLI entrypoints (like filtering to a repo)

It would be helpful to be able to open the TUI filtered to a certain view. `ghui --repo kitlangton/ghui` would open the TUI to that filtered project view. There's the potential for other entry points, like PRs filtered to a certain org.

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I've been using ghui inside a herdr pane alongside gitbutler. I have this default workspace view where I like to have ghui in the bottom left filtered down to the PRs for whatever project I'm working on. The challenge is, to get ghui filtered to the right contextual view when opening I'd need to hack together some herdr commands. Now, I'm not opposed to doing that, but it would be nice if I could just have it open to the right view from startup.

Start at the CLI entrypoint and trace how startup arguments are parsed and how the TUI selects its initial view. Define the behavior for `ghui --repo kitlangton/ghui`, then verify that startup opens the repository-filtered project view and that the argument structure can support future entry points such as organization-filtered PRs.

Written by the indexing model from the issue text.