* refactor(config): change default category from Inbox to Todo
* refactor(views): adopt markdown checkbox line format
Problem: task lines used an opaque /ID/ [N] prefix format that was
hard to read and inconsistent between category and priority views.
Header lines had no visual marker distinguishing them from tasks.
Solution: render headers as '## Cat', task lines as
'/ID/- [x|!| ] description'. State encoding: [x]=done, [!]=urgent,
[ ]=pending. Both views use the same construction.
* refactor(diff): parse and reconcile markdown checkbox format
Problem: parse_buffer matched the old ' text' indent pattern and
detected headers via '^%S'. Priority was read from a '[N] ' prefix.
apply() never reconciled status changes written into the buffer.
Solution: match '- [.] text' for tasks and '^## ' for headers.
Extract state char to derive priority (! -> 1) and status (x -> done).
apply() now reconciles status from the buffer, setting/clearing 'end'
timestamps — enabling the oil-style edit-checkbox-then-:w workflow.
* refactor(buffer): update syntax, extmarks, and render for checkbox format
Problem: syntax patterns matched the old indent/[N] format; right_align
virtual text produced a broken layout in narrow windows; the done
strikethrough skipped past the ' ' indent leaving '- [x] ' unstyled;
render() added undo history entries so 'u' could undo a re-render.
Solution: update taskHeader/taskLine patterns for '## '/'- [.]'; rename
taskPriority -> taskCheckbox matching '[!]'; switch virt_text_pos to
'eol'; drop the +2 col_start offset so strikethrough covers '- [x] ';
guard nvim_buf_set_lines with undolevels=-1 so renders are not undoable.
Also fix open_line to insert '- [ ] ' and position cursor at col 6.
* refactor(init): replace multi-level priority with binary toggle
Problem: <C-a>/<C-x> overrode Vim's native number increment and the
visual g<C-a>/g<C-x> variants added complexity for marginal value.
toggle_complete() left the cursor on the wrong line after re-render.
Solution: remove change_priority/change_priority_visual; add
toggle_priority() (0<->1) mapped to '!', with cursor-follow after
render matching the pattern already used in priority toggle. Add
cursor-follow to toggle_complete() for the same reason. Update plugin
plugs (priority-up/down -> priority) and add 'due'/'undo' to the
:Pending completion list. Update help text accordingly.
* feat(buffer): reflect current view in buffer name
Problem: no way to tell at a glance which view (category vs priority)
is active — the buffer was always named 'pending://'.
Solution: update the buffer name to 'pending://category' or
'pending://priority' on every render, so the view is visible in
the statusline/tabline without any extra UI.
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