Replace .drone.yml with .woodpecker/ pipeline configs (frontend.yml, api.yml).
Convert Drone env vars to Woodpecker equivalents (CI_PIPELINE_NUMBER, CI_COMMIT_SHA),
use woodpeckerci/plugin-git for clone with retry, woodpeckerci/plugin-slack for
notifications, and plugins/docker for image builds. Update all docs and skills.
The crawler subdirectory was the only active project. Moving it to the
repo root simplifies paths and removes the unnecessary nesting. The
vqa/ and immoweb/ directories were legacy/unused and have been removed.
Updated .drone.yml, .gitignore, .claude/ docs, and skills to reflect
the new flat structure.