Type { anywhere a value belongs: answer recall in labels, explained picker everywhere

[AllTerrainDeveloper]

What was wrong

The { value picker only existed in Notifications, Confirmations and the formula box. Field labels, hints, headings and HTML blocks had nothing, either on the canvas or in the inspector. A {field:…} typed there would also have printed literally on the live form, because tags were only resolved after submission. Adding the picker alone would have offered values that do nothing, so this PR makes them work too.

What changes

Answer recall (new front-end feature)

• {field:id} in a label, hint, heading, HTML block or consent text renders as an empty .atf-recall slot (alltfo_recall_markup(), which only touches text nodes, so an href in an HTML block stays intact). The form bundle fills the slot live from the visitor's answer. Choices show their label, composites show their non-empty parts, a total shows its computed value, and an unknown id stays visible as typed.
• Password, file, signature and repeater answers are never echoed, on either side.
• Server-side "X is required" errors read the label with the answer filled in (alltfo_recall_text()).
• The client schema now carries choice labels, which recall needs.

The picker wherever it applies

• Inspector Label, Hint, HTML and consent text: Insert an answer, with earlier answers first and later ones flagged "blank until they get there".
• Canvas inline text (label, hint, heading, toggle/consent label): typing { opens a floating picker beside the text.
• The success screen's button label now takes merge tags. The server already resolved them there.

Better explanations

• Each row shows its explanation and an "e.g." example. The catalogue always had both, but the list used to throw them away. Search also matches the explanation, and a footer teaches the { shortcut.
• Formula references say what they count as: a dropdown counts as its option's price, a switch as 1 or 0, a quiz as points. Repeater references explain sum() vs avg()/min()/max(). The formula editor explains every function on hover or focus.
• The inspector's reference line named only {field:id}, which formulas don't accept. It now gives both forms.

Bug caught in QA
The canvas repaint after an autosave didn't count an open floating picker as "editing the canvas". With the picker open for more than 2.5 s, the text a pick was about to land in got detached. The repaint now waits for the picker (pickerOwner()).

Tests

• Vitest: 541 total, 2 skipped, all others pass. New recall.test.ts covers formatting, catalogue order and exclusions, and live fill in the form bundle. Picker tests cover explanations, the canvas { flow and ownership. Formula-editor tests cover the explanations.
• PHPUnit: 799 pass. New recall.php covers slots, attribute safety, rendered label/hint, choice labels in the client schema, the password guard and the validation message.
• PHPCS clean for changed files. tsc clean.
• Manual QA on the 8889 site with the "QA pickers" form:
  • The canvas picker opens on {.
  • A pick still lands after an autosave fires mid-pick.
  • The front-end preview fills "Hi {field:name}" as "Hi Ada" while typing.
  • All QA edits were reverted.

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