fix(popup): commit volume percentage on click-outside instead of discarding

[YuriNachos]

Closes #358.

Summary

The volume percentage popover (EditablePercentage) discarded the typed value when the user clicked outside or switched apps — only pressing Return committed. A half-typed but valid number was lost on any dismissal other than Return, which reads as broken. The typed value is now committed on those dismissals instead.

Changes

• Route the click-outside / app-deactivation dismissal through commit() instead of cancel() (FineTune/Views/Components/EditablePercentage.swift).
• The commit validation already discards garbage and out-of-range input (returns nil → applies nothing, identical to the old cancel() for invalid input), so click-outside with "abc" or "500" safely applies nothing; a valid number is kept.
• Dismissal paths after this change:
  • Return = commit() (unchanged).
  • Esc = cancel() / discard (unchanged — the one explicit "abandon" path).
  • Click-outside / global click / app-deactivation = commit() (was cancel()).
• The commit validation is extracted into a pure @testable static helper committedValue(from:in:), 1:1 with the previous inline validation (same % strip, trim, Int parse, range check), so it is unit-testable headlessly. The dismissal closure captures the struct by value, so no retain cycle is introduced.
• New FineTuneTests/EditablePercentageCommitValueTests.swift covering the helper.

Testing

• xcodebuild test -scheme FineTune -skip-testing:FineTuneUITests CODE_SIGN_IDENTITY=- — TEST SUCCEEDED.
• EditablePercentageCommitValueTests (6 cases, mutation-verifiable): valid int → applied; trailing % → stripped; whitespace → trimmed; out-of-range → nil (discard, not clamp); garbage → nil; empty → nil. Removing any step of the validation flips the relevant case red.
• Manual matrix (left for owner): type a value, click outside → applied; type garbage, click outside → discarded; Esc → discarded.