Add fmt, lint, and check commands for scenario files

[lambdalisue]

Summary

• Add probitas fmt command that runs deno fmt --no-config on scenario files
• Add probitas lint command that runs deno lint --no-config on scenario files
• Add probitas check command that runs deno check --no-config on scenario files
• Introduce shared _deno.ts module for common Deno subcommand execution logic

Why

Scenario files need formatting, linting, and type-checking just like any TypeScript code, but should use the same file discovery logic as probitas run. These commands bridge Deno's tooling with Probitas' configuration-driven file discovery, allowing users to run standard Deno tooling without manually specifying files.

All three commands use --no-config to avoid conflicts with project deno.json, and lint excludes rules incompatible with scenario imports (no-import-prefix, no-unversioned-import).

Test Plan

• Run probitas fmt --help and verify help text displays correctly
• Run probitas lint --help and verify help text displays correctly
• Run probitas check --help and verify help text displays correctly
• Run each command on a project with scenario files

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