Finalize 0.3.0 task syntax and GitRepo workspace handles

[dcx]

Summary

• Allow task arguments to be passed directly as keywords to Workspace.run(...) and WorkspaceTask.run(...), with args={...} retained for explicit mappings and reserved-name escape hatches.
• Make repo: sp.GitRepo the clean writable workspace-handle spelling for tasks, while preserving explicit narrower grants such as sp.May[sp.GitRepo, sp.ReadOnly].
• Stop treating unannotated repo parameters as implicit workspace handles; they now behave like ordinary value parameters unless annotated.
• Align generated task modules, quickstart templates, workspace-handle examples, visual artifact examples, tests, and changelog entries with the 0.3.0 syntax.

Testing

• uv sync --offline
• uv run ruff check .
• uv run ruff format . --check
• uv run pytest shepherd/packages/dialect/tests/test_run_kwargs_sugar.py shepherd/packages/dialect/tests/test_register_ceiling_derivation.py shepherd/packages/dialect/tests/test_workspace_context_manager.py shepherd/packages/dialect/tests/test_workspace_control_core_loop.py shepherd/packages/dialect/tests/test_workspace_control_run_output_wrappers.py — 130 passed
• make release-evidence-beat0 — 71 passed; executed-evidence sentinel green for 19 required ids
• make release-evidence-lane-c — 10 passed; executed-evidence sentinel green for 10 required ids, 7 jailed ids skip-free

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