refactor: deduplicate PowerShell shortcut usage dispatch

[JacobOptimiza]

Problem

Invoke-DevShortcutCommand (default branch) and Invoke-DevNavigator (dev shortcut with no items) each contained the same English usage throw duplicated twice consecutively before the Spanish throw — a known copy-paste defect in the shortcut dispatch flow.

Refactor

• New private helper Resolve-DevShortcutUsageError (approved verb, not exported): consults the language and throws the exact existing EN or ES usage message.
• Both dispatch points now call the helper; the duplicated if blocks are gone. Behavior-preserving: identical messages, identical throws, same public API/exports, no config format or Rust CLI changes. (Audited the whole module for the same pattern: no other occurrences.)

Regressions

• Invoke-DevShortcutCommand too-many-args usage: EN and ES messages asserted (new).
• Invoke-DevNavigator -Command shortcut with no arguments: EN and ES usage asserted (new).
• Existing valid paths re-verified: remove, command-only, alias+command, plus persistence round-trip.

Coverage post

PowerShell commands 565/673 (83.95%), lines 360/431 (83.53%) — both gates >= 80% PASS (denominator shrank with the removed duplicate lines). Pester: 118 passed / 0 failed.

Gates

validate-powershell (parser + PSScriptAnalyzer) OK · Pester + coverage gate OK · cargo test 171 OK · node bootstrap tests OK · git diff --check OK.