Add --output flag to specify migration report file path

[Nehal-cell]

Feature request

Currently the migration report is always saved as codemorph_report.md in the current directory.

Add --output <path> flag so users can specify where the report is saved.

Example

codemorph migrate --from flask --to fastapi . --output ./reports/migration_2026.md

Files to change

• src/cli.py — add --output option to migrate command
• src/reporter.py — accept output path parameter