Remove deprecated convert CLI command in favour of export

[rushabhcodes]

Summary

Removes the deprecated tsci convert command from the CLI in favour of tsci export and cleans up the direct dependencies that were only used by that command.

Changes

• removes registerConvert from the CLI entrypoint
• deletes the deprecated cli/convert/register.ts command implementation
• deletes the dedicated convert CLI test
• removes circuit-json-to-tscircuit from direct dependencies
• removes kicad-component-converter from direct dependencies
• updates CLI help output in the README to no longer mention convert

Why

The convert command is deprecated and no longer needed in the CLI surface. Removing it also lets this package drop the direct dependencies that only existed to support that command.

Validation

• ran bunx tsc --noEmit
• ran bun run build
• confirmed bun ./cli/main.ts --help no longer lists convert
• confirmed circuit-json-to-tscircuit is no longer referenced anywhere in this repo

Notes

• kicad-component-converter may still appear in bun.lock as a transitive dependency through tscircuit, even though it is no longer a direct dependency of this package

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