v0.6.0

Rename SeekDrop to SeekSync (0.6.0)

Everywhere: app, package (src/seeksync), plugin (seeksync_bridge), data/db/log
names, SEEKSYNC_HOME, installers, CI, docs and website. The old data folder,
seekdrop.db, the old default download folder and the SeekDrop Bridge plugin key
are taken over on first start (SeekDrop added to the legacy names). The Windows
installer removes the old SeekDrop.exe and shortcuts. Tests for the migration.

Also: root vercel.json serves site/ as a static site (the repo root has a
pyproject.toml that Vercel took for a Python app), and screenshots retaken.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>