Implement Road record declarations and named constructors

[blackboxprogramming]

The documented type Device: syntax currently enters an unimplemented parser path and never finishes. This implements the next language step identified by PR #4: record syntax over the existing dictionary-based Road object model.

Changes:

• Parse record declarations and Device{name: "Lucidia"} expressions, including nested and multiline constructors.
• Reject duplicate, unknown, and missing required fields. Validate constructor shape before evaluating supplied expressions or defaults.
• Evaluate explicit values in caller scope, then omitted defaults in declaration scope. Literal mutable defaults are fresh per construction; referenced mutable values retain normal sharing.
• Preserve ordinary dictionary behavior, existing verb dispatch, permission-as-data boundaries, and type annotations as metadata.
• Handle expression grouping without corrupting surrounding block indentation; report malformed delimiters with source locations.
• Add a runnable example, semantics documentation, and 31 regression cases.

Validation on Python 3.12.14:

• Before the change: 61 tests passed, 1 pre-existing skip. The new CLI regression failed with a 5-second timeout on the parser stub.
• After the change: python -m pytest tests/ -q — 92 passed, 1 pre-existing skip.
• python3 roadc.py run examples/record_types.road printed Lucidia / False / 1 / 0.
• Example parse, py_compile for changed Python files/tests, and git diff --check passed.
• Published Git tree bf146b82a9205d1027c7cc9f43f62c3f52e5b7a3 matches the locally verified tree exactly.

Boundaries:

• Python interpreter support only; the C compiler is unchanged.
• Field annotations are retained but do not enforce value types or later assignments.
• Record data does not authenticate identities, grant authority, resolve Routes, or dispatch providers/devices. Default expressions keep ordinary Road expression effects.
• The existing skipped else parsing test remains skipped. This does not claim to fix other parser stubs.

Continuity:

• Stacked on PR #4, branch work/road-object-model, pinned parent f0ea7961abac1dcdf568bec8e22b8543fae28b5d.
• New commit: a143553a89e1e33e6799209156a120223a72e4ff.
• PR Road object model: compose state, capabilities, identity, and verbs #4 remains open and unchanged. Merge/reconcile that foundation first, then retarget and reconcile this draft against main.
• Existing workflow filters target main; this stacked draft is locally verified and does not claim a hosted CI pass.