feat: make keyboard shortcuts safe in text-entry contexts

[martinshub-tech]

Closes #1422

Here is what I did:

Created a robust utility function isTextEntry in
lib/keyboard.ts
to deterministically check whether an event target is an input (excluding buttons/checkboxes), textarea, select, or contenteditable element.
Updated
app/components/ShortcutsOverlay.tsx
so the ? shortcut no longer triggers while typing in a text field.
Updated
app/ReceiptCard.tsx
to use the new isTextEntry function for its c and m shortcuts, hardening it across all contexts (including content editables).
Updated
app/CreateStreamForm.tsx
to ensure the Alt+R and Alt+A shortcuts do not steal focus if the user happens to press them (or AltGr variants) while actively typing in a different text field, while maintaining their navigational intent outside of text entries.
Ran the relevant unit tests (such as app/CreateStreamForm.test.tsx and app/components/ShortcutsOverlay.test.tsx) locally, which all passed.

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