to_obsidian and to_canvas built note filenames from node labels with no
length cap, so a label >=255 bytes crashed write_text with OSError. Add a
shared _cap_filename helper that caps on UTF-8 bytes (not chars, so CJK
labels don't slip past) and appends an 8-char hash of the full label when
truncating, so two distinct labels sharing a long prefix stay distinct.
Both safe_name builders route node, community and canvas filenames through
it; wikilinks stay consistent because they read the same filename dict.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
