fix: display None for empty distribution frequency

[daggerok]

Scope

Replace the existing formatted Frequency placeholder 00 - — with 00 - None.

• Literal-only UI/updater changes where applicable; existing explicit Unknown and all other cadence mappings unchanged.
• Existing persisted JSON changes are limited to derived Frequency label strings; no financial data refresh, schema changes, or inference changes.
• Update existing expectations and add a regression test of the actual formatter/helper.

Validation

• Bun tests: 92 pass, 0 fail.
• Bun updater build and app build passed.
• Exact replacement, JSON field-path, clean worktree and diff-whitespace guards passed.

The owner explicitly authorized creating and merging these narrow Frequency code PRs. Aberdeen PR #1 remains open and is not part of this merge authorization.