fix: track open dict copy keysets

[ApexWorm]

Problem

The Python dict-key detector treated dict copies of externally supplied mappings as closed schemas. Reads of valid runtime keys were then reported as phantom reads and near misses.

Fix

Track keyset provenance through dict literals, dict constructors, tracked aliases, copy calls, unpacking, updates, and dynamic writes. Suppress phantom and near-miss findings only when the resulting keyset is open; retain typo detection for closed local schemas.

Verification

• 42 focused and related dict-key detector tests passed
• Ruff, py_compile, and diff checks passed
• Live validation removed phantom findings from three representative external-mapping copies in the Frequency Coordination System repo
• Full suite: 5,809 passed, 4 skipped; the two failures are duplicate instances of a pre-existing review-prompt assertion reproduced on pristine main