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.

scripts/demo-init.lua

@@ -1,30 +0,0 @@
-vim.opt.runtimepath:prepend(vim.fn.getcwd())
-local tmpdir = vim.fn.tempname()
-vim.fn.mkdir(tmpdir, 'p')
-
-vim.g.pending = {
-  data_path = tmpdir .. '/tasks.json',
-}
-
-local store = require('pending.store')
-store.load()
-
-local today = os.date('%Y-%m-%d')
-local yesterday = os.date('%Y-%m-%d', os.time() - 86400)
-local tomorrow = os.date('%Y-%m-%d', os.time() + 86400)
-
-store.add({
-  description = 'Finish quarterly report',
-  category = 'Work',
-  due = tomorrow,
-  recur = 'monthly',
-  priority = 1,
-})
-store.add({ description = 'Review pull requests', category = 'Work' })
-store.add({ description = 'Update deployment docs', category = 'Work', status = 'done' })
-store.add({ description = 'Buy groceries', category = 'Personal', due = today })
-store.add({ description = 'Call dentist', category = 'Personal', due = yesterday, priority = 1 })
-store.add({ description = 'Read chapter 5', category = 'Personal' })
-store.add({ description = 'Learn a new language', category = 'Someday' })
-store.add({ description = 'Plan hiking trip', category = 'Someday' })
-store.save()

scripts/demo.tape

@@ -1,28 +0,0 @@
-Output assets/demo.gif
-
-Require nvim
-
-Set Shell "bash"
-Set FontSize 14
-Set Width 900
-Set Height 450
-
-Type "nvim -u scripts/demo-init.lua -c 'autocmd VimEnter * Pending'"
-Enter
-
-Sleep 2s
-
-Down
-Down
-Sleep 300ms
-Down
-Sleep 300ms
-
-Enter
-Sleep 500ms
-
-Tab
-Sleep 1s
-
-Type "q"
-Sleep 200ms