feat(todo): recurring tasks, set through a picker (ADR 0033, D7)

A task's date may recur: every n days, weeks (on which weekdays),
months (on its day, or its nth or last weekday), years, from its date
or from when it is done, until a day or for n times. Done, it moves on
to the next day after both its date and today, its deadline as far, its
time kept, its done sub-tasks open again and when it was done kept in
its payload; undo writes all of it back. The date sheet offers the rules
that fit the task's day and a rule of the person's own; rows show a
recurring date with its own icon, the task sheet the rule in words.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0033-halkyon-todo.md

@@ -1,8 +1,8 @@
 # ADR 0033: Halkyon Todo, what it does and how it looks
 
 - **Status:** decided 1 Nov 2026, by the developer (D1–D10 below, the agent's
-  recommendations taken as a whole). Built the same day: steps 1 to 3 and Today and
-  Upcoming as lists (step 4 without recurrence, reminders and the week strip).
+  recommendations taken as a whole). Built the same day: steps 1 to 3, Today and
+  Upcoming as lists, and recurrence (step 4 without reminders and the week strip).
 - **Numbering:** 0025–0029 are held (ADR 0030's note), 0032 is Jellyfin's; this is the
   next free number.
 - **Builds on:** ADR 0030, D7, D12, D14, D15 and D60 (Train's sealed rows, its shell, its
@@ -102,6 +102,17 @@ the rail, a wash of strawberry, settings grouped as theirs. What the screenshots
   or the nth weekday), years, from the date or from completion, until a day or for n
   times. Dates and tokens typed into quick add ("tomorrow 6am", "every Monday", `#project`,
   `p1`), in English and German, are a later step, built on the same rule.
+  As built (1 Nov): the rule is part of the task's date (`Repeat` in `TaskDate`, its
+  payload's `date.repeat`), so a task without a date doesn't recur and clearing the date
+  ends it; schema 1 holds it, as no task was written before. Done, a task counted from its
+  date moves to the rule's first day after both its date and today (an overdue one isn't
+  moved onto a day already past), counted from completion it moves the rule's units on
+  from today, on no particular weekday; its deadline moves as far, its time is kept, its
+  done sub-tasks open again, and when it was done is added to its `completions`. Undo
+  writes back every task that changed. The picker offers the rules that fit its day
+  (every day, every weekday, its weekday, its day or nth weekday of the month, its day of
+  the year) and a rule of the person's own; weeks start on Monday for every n weeks, until
+  the week's first day is a setting (D4).
 - **D8 The first version** (recommended): Inbox and projects with sections, shown as a
   list; sub-tasks; Today (Overdue first, rescheduling them together, then today's); Upcoming
   as an agenda with the week strip opening into the month; the task sheet (rows for the