fix: nonfatal missing key commands (resolves #6397)j

[ariane-emory]

This PR changes the behaviour so that binding missing key commands in a user's config is not a fatal error that prevents the startup of opencode entirely.

With this PR, keybindings for non-existent keywords, when struck will instead display a toast saying "No command 'the_fake_command_name'".

Resolves #6397.

[rekram1-node]

this shouldn't be enforced on the tui side, I would expect the tui to always be fed a valid config, and maybe u can introduce a config event for warnings that you emit that the tui could display

[ariane-emory]

@rekram1-node Alright, I'll look into how that could work and see what I can come up with.

[ariane-emory]

@rekram1-node Well.... it turned out to be a lot trickier to do than I thought it would, but after a few rerolls this does seem to be doing it in the way that you'd requested?

• strips the 'unknown' key commands out prior to validation, so the config always receives a valid config.
• -emits a config.warning BusEvent that TUI then consumes and reacts to by displaying a warning like Unknown key commands: foo, bar.
• retains the Unknown key command: foo toast upon striking one of these keys.

Whaddya think? If there are further refinements you'd like. don't hesitate to ask!

[github-actions[bot]]

Hey! Your PR title Fix: nonfatal missing key commands (resolves #6397) doesn't follow conventional commit format.

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[ariane-emory]

Requires further testing/revision after significant recent changes in dev, re-drafting until that's been done.