ci: migrate to woodpecker

[BryanChasko]

summary

• moved ci workflow from github actions to woodpecker pipeline
• cargo test, clippy (strict), fmt check unified in single step
• readme-lint now pr-gated with changed files detection via git diff

migrated

• cargo test + cargo clippy + cargo fmt check
• pr-conditional readme-lint step with git-based file filtering

not migrated

• github actions caching layers (not needed for woodpecker on persistent runner)

unresolved

• woodpecker endpoint must be registered in ops repo before pull
• assume rocm-aibox runner has rust:1-slim image available