Show blueprint source path in blueprint list

[jeremybeard]

What

Adds a Location column to blueprint list so users can immediately see which file each blueprint is defined in.

• When --template-dir DIR is provided, the path is rendered relative to DIR.
• Otherwise it is rendered relative to the current working directory.

This addresses feedback that it was unclear where a given blueprint actually lives — the registry already tracked locations, but blueprint list never surfaced them.

Example

$ blueprint list --template-dir examples/advanced/dags/

                              Available Blueprints
┏━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━━━━━━━┓
┃ Name     ┃ Versions ┃ Description                   ┃ Class    ┃ Location       ┃
┡━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━━━━━━━┩
│ analyze  │ 1        │ Run signal analysis ...       │ Analyze  │ blueprints.py  │
│ orbit    │ 1        │ Calculate and execute ...     │ Orbit    │ blueprints.py  │
│ scan     │ 1, 2     │ Multi-band scan with ...      │ ScanV2   │ blueprints.py  │
│ transmit │ 1        │ Transmit data to a ...        │ Transmit │ blueprints.py  │
└──────────┴──────────┴───────────────────────────────┴──────────┴────────────────┘

Here the locations are shown relative to the supplied --template-dir (so blueprints.py rather than examples/advanced/dags/blueprints.py). The shown path is the location of the latest version (matching the Class column).

How

• The registry previously stored locations relative to an internal base directory, which is not meaningful when shown at the CLI. It now stores the resolved absolute path.
• New blueprint/utils.py::display_path(path, base=None) renders a path relative to base (defaulting to the cwd), falling back to the absolute path when the file is not under base (e.g. a sibling tree, or a different drive on Windows). The list command passes the resolved --template-dir as base when one is given.
• DuplicateBlueprintError / MultipleDagArgsError render their messages lazily in __str__, so locations are resolved relative to the cwd at display time rather than baked in when the error is raised. They pass their raw args to super().__init__() so repr() stays informative and the exceptions remain picklable.

Tests

• tests/test_utils.py::TestDisplayPath — display_path under/outside the base, and the explicit-base override.
• tests/test_registry.py::TestBlueprintLocations — list_blueprints() reports absolute locations.
• tests/test_cli.py::test_list_location_is_relative_to_template_dir — the Location column renders relative to --template-dir.

All unit tests, ruff, and ty pass.