Codex/fix review findings

[ColumbusLabs]

What

Why

Mock-first quality

• Mock data covers the change. If this PR introduces a new
  provider behavior, error state, multi-account scenario, or cost
  dashboard surface, a corresponding mock is added/updated in
  Sources/CodexBar/Sync/MockProviderInjector.swift (or a comment
  here explains why no mock is needed).
• Mock tests pass locally. swift test --filter "MockProviderInjector" shows ≥55 tests passing.
• No regression in existing mocks. swift test --filter "Sync|MockProviderInjector" shows ≥136 tests passing.
• Mock toggle still safe to flip. Activating + deactivating
  the mock toggle (Settings → Mobile → Debug · Mock Provider Data)
  doesn't pollute real data.

Other Quality Gates

• swift test passes (full suite).
• ./Scripts/lint.sh lint passes (0 violations).
• ./Scripts/lint.sh format shows no changes (or commits the
  format result).
• If touching iOS, xcodebuild build and full iOS test suite
  pass on iPhone 17 Pro simulator.
• If touching the cost JSONL parser, parserLogicVersion was
  bumped (CI lint enforces this).

Risk + Rollback

• Blast radius:
• Rollback plan:

Screenshots / Logs (if UI / behavior change)