Add source period metadata to Arch facts

[MaxGhenis]

Summary

• add optional period metadata to Arch canonical facts: start/end dates, period basis, authority, source label, and accounting basis
• propagate the metadata from source-package YAML through source-record specs and fact construction
• store the metadata in the relational Arch DB schema and concept-alignment rows

Why

Microplex needs target sources to distinguish calendar, tax, fiscal, projection, and cash/accrual semantics without overloading the coarse period_type/period pair. This keeps those semantics in Arch source packages rather than in downstream calibration glue.

Validation

• uv run ruff check arch/core.py arch/sources/specs.py arch/source_package.py arch/database.py tests/test_arch_core.py tests/test_arch_source_package.py tests/test_arch_database.py
• uv run pytest tests/test_arch_core.py tests/test_arch_source_package.py tests/test_arch_database.py