Cleanup Makefile & Improve Dev Experience

#### Problem
- The repo has both a `Makefile` and a `Taskfile.yml`, with redundant commands. We should standardize on `Taskfile.yml` and remove `Makefile`.
- Scripts are split between `scripts/` and `hack/`, and they don’t work well together.
- Running the plugin locally is a pain—too many steps, not well-documented.

#### Proposed Fix
- Remove `Makefile` to avoid duplication.
- Organize scripts in a single, consistent place.
- Improve local dev setup so it’s easier to run and debug.
- Document the procedure to run a test deployment of the local code.

Compare Makefile with Taskfile.yml, then inventory the scripts/ and hack/ directories and the current local plugin run steps. Done means redundant task commands are removed, scripts have one consistent home, local execution and debugging are documented, and the test-deployment procedure is documented.

Written by the indexing model from the issue text.