Add tap source install target derivation

[eric-tramel]

What

Implements concrete source generation and validation for all [tool.ddp.tap].default-source modes in the ddp catalog tooling.

• PyPI sources generate {"type": "pypi", "package": <package>}.
• Git sources generate {"type": "git", "url": <repository-git-url>, "ref": <release-ref>, "subdirectory": <package.path>}.
• Path sources generate {"type": "path", "path": <package.path>, "editable": true}.
• Catalog consumers can now derive a structured install target from source metadata via InstallTarget and install_target_for_source_metadata.

Why

Tap catalog schema v2 needs source objects that are concrete enough for Data Designer install flows. The generated catalog also needs to reject malformed source configuration early so invalid tap metadata does not publish unusable install instructions.

Usage

For the default NVIDIA tap config, catalog output remains PyPI-only:

{
  "source": {
    "type": "pypi",
    "package": "data-designer-template"
  }
}

For an external tap configured with Git sources:

[tool.ddp.tap]
default-source = "git"
repository-git-url = "https://git.example.test/acme/dd-plugins.git"
release-ref-template = "{package}/v{version}"

A package named data-designer-example at version 0.2.0 derives this install target:

data-designer-example @ git+https://git.example.test/acme/dd-plugins.git@data-designer-example/v0.2.0#subdirectory=plugins/data-designer-example

Path sources return an install plan such as:

InstallTarget(target="plugins/data-designer-example", editable=True)

How

• Makes repository-git-url and release-ref-template Git-source requirements instead of global tap requirements.
• Adds reusable package path validation for generated package.path, Git subdirectory, and path path fields.
• Keeps source generation package-scoped so all runtime plugin entries from a multi-plugin package share the same source object.
• Adds install-target derivation for PyPI exact pins, Git PEP 508 direct refs, and editable local path plans.

Validation

• make sync
• uv run pytest devtools/ddp/tests/test_catalog.py devtools/ddp/tests/test_tap_config.py -q
• uv run ruff check devtools/ddp/src/ddp/catalog.py devtools/ddp/src/ddp/tap_config.py devtools/ddp/tests/test_catalog.py devtools/ddp/tests/test_tap_config.py
• uv run ruff format --check devtools/ddp/src/ddp/catalog.py devtools/ddp/src/ddp/tap_config.py devtools/ddp/tests/test_catalog.py devtools/ddp/tests/test_tap_config.py
• make catalog
• make check-catalog
• make check