Refactor command detection list to use a single unified source

[insign]

This PR unifies the command_starters array used for detecting shell commands. Previously, a duplicated, slightly shorter list was hardcoded in src/cli/mod.rs while a more complete list existed as COMMAND_STARTERS in src/providers/mod.rs. Making the constant public ensures consistency and reduces code duplication.

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PR created automatically by Jules for task 359382809472215330 started by @insign

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