fix(prose): work off the prose backlog and make the gate blocking

[astrapi69]

Summary

This works off the prose backlog that .github/quality-state.json recorded on 2026-09-23 and makes the prose gate blocking.

1. Gate files from adaptive-learner-content-template#95 (97a2dcc), byte for byte. The gate stops reporting typing variants in accept, YAML tags, the surnames Weiss and Gross, French grosse, and code syntax in plain-text fields.
2. Backlog. Umlaut findings: 19 with the old gate.
   • 4 were real misspellings, in docs/export-set-usage.de.md. Each is fixed at the reported line with the spelling the gate names.
   • tests/test_export_set.py asserted that a misspelling does not appear in the export, so it held the misspelling on purpose. The assert now derives it from the correct word ("Übungen".replace("Ü", "Ue")), and the ASCII slugs in its comments are in backticks (1 line(s)).
   • 09-dictionaries.json, a card hint: items() liefert (schluessel, wert)-Tupel. becomes items() liefert Tupel aus Schlüssel und Wert.
   • 02-jsx.json, a card note: setzt den Wert der Variablen gruss ein becomes setzt den Wert dieser Variablen ein
   • 04-state-usestate.json, a prompt (rendered as Markdown): the code const [zaehler, setZaehler] = useState(0); goes into backticks, as the lesson's theory already writes it
   • The rest were false alarms that the new gate no longer reports.
   • Em dashes: 204, replaced with the strategy of adaptive-learner-content#201 and alc-psychology#48, most specific rule first:
     • a spaced aside or pause in running text becomes a comma: 133
     • a title, title_native, name or card front field, a Markdown heading, a comment line or a media title becomes -: 54
     • after code (), ], ', a backtick) it becomes -, so the comma cannot read as code: 9
     • a list item - **Term** — text becomes - **Term**: text: 8
3. The gate blocks. .github/quality-state.json is removed (it held only the prose-gate exception). An absent file means blocking.

Verification

• All 204 changes were made by a script and checked by a second one:
  • every hunk sits on a former em dash;
  • no em dash is left;
  • every JSON file parses;
  • every Markdown heading and every title and front field that had an em dash now has -.
• The before/after pairs were also read by hand, in random samples per rule.
• None of the changes is in a code, accept, distractors or tiles field.
• Gates, in this branch: see the test plan.

Test plan

Gate	Result
make lint	engine-validate: 36 lesson(s), 5 manifest(s) checked - 0 file(s) with errors
make validate	All 4 set(s) passed validation.
make stable-ids	checked: 628 base id(s) / 628 head id(s), 36 base lesson(s) / 36 head lesson(s), 0 base retired / 0 head retired stable-id coverage: 4 of 4 set(s) fully minted,
pytest	199 passed, 1 skipped, 10 warnings in 4.81s
make prose-check	prose gate: 102 tracked file(s) clean

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