ci: migrate release automation and workspace packaging

[Copilot]

This updates release automation to use release-please manifest mode for the multi-package repo and replaces the old workspace.toml setup with a standard root Poetry aggregator layout. It also raises the Airflow baseline to a patched release and aligns a few compatibility shims with the updated workspace/tooling behavior.

• Release automation

  • Switches .github/workflows/release-please.yml from single-package Python mode to command: manifest.
  • Adds .release-please-manifest.json and release-please-config.json to track packages/core, packages/plugins-workflows, and packages/providers-airflow explicitly.
  • Keeps release metadata aligned with actual package directories instead of relying on a nonstandard version-file.

• Root Poetry workspace

  • Removes workspace.toml.
  • Promotes the root pyproject.toml to the canonical workspace definition with package-mode = false.
  • Declares local path dependencies for the repo-managed packages so Poetry and CI tooling can resolve the workspace from standard metadata.

• Package dependency wiring

  • Converts cross-package development dependencies to local path dependencies where appropriate.
  • Refreshes poetry.lock against the new root dependency graph.

• Airflow security baseline

  • Raises the Airflow provider package dependency floor from apache-airflow >=2.8.0 to >=3.2.0.
  • Updates install docs/examples to reflect the patched Airflow requirement.

• Compatibility cleanup

  • Consolidates optional Airflow fallback types into a shared compatibility shim for providers code.
  • Adjusts a small optional tracing/type-handling path in core so the stricter workspace validation flow remains consistent.

# .github/workflows/release-please.yml
with:
  command: manifest

# pyproject.toml
[tool.poetry]
package-mode = false

[tool.poetry.dependencies]
imednet = { path = "packages/core", develop = true }
imednet-workflows = { path = "packages/plugins-workflows", develop = true }