Release socketry-markdown v0.1.0

[samuel-williams-shopify]

Summary

• Adopt the shared Socketry Rust project standards and automation.
• Set the fork's package baseline to 0.0.0 and prepare the first release as 0.1.0.
• Allow the initial version to be lower than the upstream fork point when crates.io has no newer published version, while preventing downgrades below versions already published.

Release validation

• cargo bake cargo:release
• GitHub Actions will run formatting, Clippy, tests, and coverage for this revision.

After this reviewed change is merged, the first crates.io upload and trusted publisher registration will use the documented bootstrap on aiko.local.