fix(booth): a partial ask answer is recorded, not refused

Operator: the form failed when a question was left blank. Refusing the whole
submission over one blank threw away the picks that were made, and the HTML
`required` on the radios blocked it in the browser before the server saw it.

- answered questions recorded; blank ones land in `unanswered`; `complete` says
  whether the set is finished; a blank question carrying a note keeps the note
- `required` dropped from both templates so the browser cannot block a partial
- refused only when there is no pick anywhere AND no notes (a 400 — that would
  flip an open ask to answered with no decision recorded); a choice outside the
  option list is still an error
- new ◐ partial state with an n/N count; skipped questions render as skipped
- README + global CLAUDE.md tell reading sessions to check `complete`
- 154 tests; v0.1.15

README.md

@@ -141,8 +141,14 @@ EOF
 #    "choice_index", "label", "notes"}, "r2": {...}, "seed": {...}}, "notes", "answered_at", "answered_by"}
 ```
 
+Both shapes also carry **`unanswered`** (the question keys left blank; `[null]`
+for a blank single-question ask) and **`complete`** (false until every question
+has a pick). A reading session should check `complete` before acting on a
+multi-question answer, and treat a key in `unanswered` as "not decided", never
+as "declined".
+
 The single-question answer: `{"stem", "prompt", "choice", "choice_index", "label", "notes",
-"answered_at", "answered_by"}` — `choice` is the option id (the label itself
+"unanswered", "complete", "answered_at", "answered_by"}` — `choice` is the option id (the label itself
 for string options), `choice_index` its 0-based position, `answered_by` the
 client address. `POST /b/<name>/answer` is what the form submits — fields `ask` plus
 `choice` / `notes` (single) or `choice.<key>` / `notes.<key>` / `notes` (multi);
@@ -156,6 +162,19 @@ Rules of the primitive:
   `questions` when the picks belong together and should land as one answer.
 - **Re-answering overwrites.** The sidecar is the *current* answer, not a log.
   The page shows the recorded answer with a collapsed *change answer* form.
+- **Blanks are legal — a partial answer is recorded, not refused.** Leaving a
+  question alone is a real outcome ("none of these", "not listened to yet"), and
+  refusing the whole submission over one blank threw away the picks that WERE
+  made. So every answered question is recorded, every blank one lands in
+  `unanswered`, and `complete` says whether the set is finished. The radios carry
+  no HTML `required`, so the browser does not block the submit either. A question
+  left blank but carrying a note keeps the note (`choice: null`). The one refusal
+  is a submission with **no pick anywhere and no notes** — a 400, because it would
+  flip an open ask to "answered" while recording no decision, which is worse for
+  the reading session than leaving it open. A choice that is not in the option
+  list is still an error: that is a broken form, not a skipped question.
+  Partially-answered asks show as `◐ partial` with an `n/N` count; re-submitting
+  fills in the rest.
 - **Open asks are flagged** — an amber `? N asks` badge on the index card and in
   the booth header — so a waiting question is visible from the front page.
 - **A broken ask is shown as broken**, not hidden: if the JSON does not