v0.5.0 — snippet library linking + portability

Added

• The snippet library is now a true source of truth. Pasting a snippet
  onto a button (or saving it to the library) now links them by reference:
  editing a snippet in the library updates every button that uses it. Edit the
  text on the button itself and it detaches into a separate copy. The "used by
  N actions" counter and the delete warning finally show the truth instead of
  always zero.
• The Library tab gained tags, notes, search by name/text, alphabetical
  sorting, text preview on the card, duplication, and export/import of the whole
  library to .json.
• Profile export now carries linked snippets along — buttons that reference
  the library survive a move to another machine.
• Undo-step coalescing: typing in the name/text field now collapses into a
  single Undo step instead of one step per character.

Fixed

• Deleting a snippet no longer breaks the buttons that used it — the text is
  inlined back into every linked action.
• Adding a snippet no longer risks rolling back unsaved edits (an empty
  snippet failed whole-config validation).
• Removed the paste-mode selector — it had no effect on behavior.

Accessibility

• Modals return focus to the element that opened them and describe their body
  for screen readers; destructive confirmations are announced as alert dialogs.
• Removed invalid <label> nesting around toggles.

---

The portable build includes the WebView2 bootstrapper; the data/ directory
(config.json, logs, snapshots) is not part of the archive and is created on
first launch.