Support configurable auto-paste shortcuts

[SeoFood]

Follow-up from #245: #245 (comment)

A user found that TypeWhisper insertion failed in Windows Terminal when their terminal paste action was bound to Shift+Insert. After changing the terminal paste shortcut back to Ctrl+V, TypeWhisper inserted text correctly.

TypeWhisper currently assumes the target app accepts Ctrl+V for auto-paste. That default should stay unchanged, but users who customize their target application's paste binding may need a configurable paste shortcut.

Possible shape:

• Keep Ctrl+V as the default auto-paste shortcut.
• Allow choosing at least Ctrl+V and Shift+Insert for the paste input TypeWhisper sends.
• Consider whether this belongs in global settings first, with per-target-app/profile overrides later.
• Update the settings UI text so it no longer hardcodes Ctrl+V when a different shortcut is selected.

Acceptance criteria:

• Auto-paste still works with the existing default behavior.
• Users can select an alternate paste shortcut without disabling auto-paste.
• The selected shortcut is used consistently by dictation, history retry/copy-last flows, workflow palette output, and HTTP/API-triggered insertion where auto-paste is enabled.
• The setting is persisted and reflected accurately in the UI.

[SeoFood]

Windows does not provide a reliable, application-independent way to detect a target application's configured paste shortcut. We also do not want to add another global or per-workflow setting for this edge case, so we are closing this as not planned. The existing workaround is to keep Ctrl+V configured as a paste shortcut in the target application.