Feat: bank / pattern import / export feature + documentation

docs/tutorials/sharing.md

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+# Sharing
+
+Export and import patterns or entire banks via the clipboard. Data is serialized into a compact text string you can paste anywhere -- a chat message, a text file, a note.
+
+## Export
+
+Press `g` to copy the current pattern to the clipboard as a share string. The string starts with `cgr:` followed by compressed data.
+
+On the patterns page, `g` exports a pattern or a bank depending on which column the cursor is in. Bank strings start with `cgrb:`.
+
+## Import
+
+Press `G` to import from the clipboard. The share string is decoded and the result replaces the current pattern.
+
+On the patterns page, importing into the banks column replaces an entire bank. Because this is destructive, a confirmation prompt appears first.
+
+## Undo
+
+Both pattern and bank imports are covered by undo. Press `u` to revert an import.