docs: update vimdoc for sync refactor, remove demo scripts

Problem: Docs still referenced openssl dependency, defaulting to `sync`
action, and the `calendar` config field. Demo scripts used the old
singleton `store` API.

Solution: Update vimdoc and README to reflect explicit actions, per-
category calendars, and pure-Lua PKCE. Remove stale demo scripts and
update sync specs to match new behavior.

README.md

@@ -7,7 +7,7 @@ Edit tasks like text. `:w` saves them.
 ## Requirements
 
 - Neovim 0.10+
-- (Optionally) `curl` and `openssl` for Google Calendar and Google Task sync
+- (Optionally) `curl` for Google Calendar and Google Task sync
 
 ## Installation