feat: add GDPR data export (download data) button (#198)

* feat: add GDPR data export (download data) button

Wires up the previously disabled "Download data" button on the settings
page. Downloads a zip with a profile.xlsx (account + owned seasons), and
per owned season a folder with each quiz's xlsx (questions, results,
eliminations tabs) and a candidates.xlsx (candidates + season info tabs).
Soft-deleted rows are included and flagged so the export reflects
everything the app still holds about the user.

* feat: include question bank in GDPR data export

Adds a question-bank.xlsx per season folder with Questions (bank
questions, answers, reusable/complete flags, labels, and which quizzes
they've been used in) and Labels tabs, since BankQuestion/BankAnswer
content was previously missing from the export.

* fix: hard-delete quiz/audit-log data when deleting an account

QuizCandidate, GivenAnswer, and Elimination are Gedmo\SoftDeleteable, so
cascading their removal through Season -> Quiz/Candidate only set
deletedAt instead of physically deleting the row. Since Candidate and
Answer are hard-deleted via orphanRemoval, this broke their foreign keys
and rolled back the entire account deletion whenever a candidate had
actually participated in a quiz. Bulk DQL deletes now purge these rows
before the cascade runs.

Also purge BankQuestion audit-log rows (ext_log_entries), which store
the editor's username/email but aren't foreign-keyed to the entity they
log, so they were never cleaned up and would otherwise keep a deleted
user's email around indefinitely.

* style: make the download data button primary (blue)

* feat: add raw answers crosstab to quiz export

Adds a "Raw answers" tab to each quiz xlsx: one row per candidate, one
column per question, with the given answer text in each cell — the raw
data behind the aggregated Results tab.

* i18n: translate new settings page string to Dutch

* refactor: sanitize filenames with Symfony's AsciiSlugger instead of a hand-rolled regex

Extracts a shared Tvdt\Helpers\FilenameSanitizer (backed by
symfony/string's AsciiSlugger) and uses it everywhere user-controlled
text (season/quiz names, account email) ends up in a zip entry path or
a downloaded filename. AsciiSlugger is allowlist-based (only A-Z/0-9
survive; everything else, including unicode and path-traversal
sequences, is folded or stripped) rather than a denylist of "unsafe"
characters, and it's an officially maintained Symfony component already
present as a transitive dependency.

Also fixes BackofficeController::exportQuiz(), a pre-existing endpoint
that built its Content-Disposition filename directly from an
unsanitized quiz name — the same class of risk the data export already
guarded against.

Naming note: sanitized names are now slugs (spaces become dashes,
unicode is ASCII-transliterated), e.g. "Krtek Weekend" -> "Krtek-Weekend".

* fix: check ZipArchive open/close results and clean up temp files on failure

Addresses CodeRabbit findings on the GDPR export:
- ZipArchive::open() and close() can both return false without
  throwing; neither was checked, so a failure silently produced an
  empty or corrupt zip, and the temp zip path was never cleaned up on
  a mid-build exception.
- writeToTempFile() leaked its tempnam()'d file if Writer\Xlsx::save()
  threw before the caller could track it for cleanup.

* fix: drop public link identifier from the candidates export sheet

The nameHash is a public quiz-access token, not something a data
export should hand out — remove it from candidates.xlsx.

* feat: add Quiz info tab covering dropouts, finalization, and disabled questions

An entity-by-entity audit of the export vs. delete flows found the
delete flow fully covered, but three Quiz/Question fields missing from
the export: dropouts, finalizedAt, and Question.enabled. Adds a new
"Quiz info" tab (first sheet) to each quiz's xlsx with this data,
without touching the shared fillQuestionsSheet() used by the existing
single-quiz template export/import feature.

Deliberately left out per user decision: the BankQuestion audit log
(would leak other owners' emails, consistent with hiding co-owner
identities elsewhere in this export) and a few low-value timestamp
fields already covered by existing Started/time-taken columns.

* feat: require a confirmed email before exporting data

Antispam measure: both the full data export (SettingsController::downloadData)
and the single-quiz export (BackofficeController::exportQuiz) now redirect
with a flash warning instead of exporting when the account's email isn't
verified yet. Adds a matching hint on the settings page next to the
download button.

composer.lock

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