Summer cleanup: XLSX export, WIDM-style quiz UI, CSS fixes (#162)

* Add CLAUDE.md, replace Makefile with Justfile, remove .junie

- Add CLAUDE.md with project overview, commands, architecture, and domain entity docs
- Remove Makefile in favour of the existing Justfile
- Remove .junie/AGENTS.md (knowledge transferred to CLAUDE.md)
- Update .gitignore: drop .junie/ entries, add .claude/settings.local.json
- Minor doc fixes in config/reference.php (typo, type correction)

* Clean up templates and CSS

- season.html.twig: remove dead empty column, drop redundant flex-row
- tab_overview.html.twig: extract Twig macro for confirm modals, fix duplicate aria-labelledby IDs
- tab_result.html.twig: remove dead comment, replace inline widths with CSS classes, simplify nested row/col forms to d-flex gap-1
- backoffice.scss: add col-result-xs/sm/md column width classes
- quiz.scss: replace broken display:grid + justify-self:center with flexbox centering

* Implement quizToXlsx() export and add export button

- QuizSpreadsheetService: implement quizToXlsx() as the inverse of
  fillQuizFromArray() — writes quiz questions and answers to XLSX using
  the same column layout as the import template
- BackofficeController: add exportQuiz() action at GET /backoffice/quiz/{quiz}/export
- tab_overview.html.twig: add Export to XLSX button in Quick actions

* Add unit tests for QuizSpreadsheetService

7 tests covering generateTemplate(), quizToXlsx(), and xlsxToQuiz():
- valid XLSX output and MIME type
- template without example reimports as empty
- template example data survives a reimport
- round-trip (export → reimport) preserves questions, answers, and correct flags
- empty quiz exports and reimports cleanly
- invalid MIME type throws InvalidArgumentException
- question with no answers throws SpreadsheetDataException with error list

* Fix quiz page vertical centering regression

The CSS cleanup broke vertical centering: flex on body causes main to
stretch full-width; place-items:center on a grid body only centers
items within their auto-sized track (not the track within body).

Fix: move background/color to html (full-viewport grid that centers
body), give body height:100% + display:grid + align-content:center
(centers the content track within full-height body) + justify-self:center
(shrink-wraps body width). Matches production behavior exactly.

* Improve quiz page layouts: WIDM-style answers and responsive centering

- Add green square answer buttons styled after the TV show
- Two-column answer grid for 6+ answers, single column on mobile
- fit-content centering for question pages so block matches question width
- Narrow fixed-width centering for form pages (enter name, select season)

* Use HeaderUtils::makeDisposition() for safe Content-Disposition filename

* Fix quizToXlsx to support unlimited answers and add header count tests

- Replace hardcoded 6-column arrays with dynamic Coordinate arithmetic
- Write data rows first to determine max answer count, write headers last
- Replace try/catch ErrorException in fillQuizFromArray with array_key_exists
- Add data-provider test covering 2, 6, 7, and 10 answers
- Add cross-question max-header and 7-answer round-trip tests

* Fix Sass healthcheck

* Improve quiz layout: add fixed topbar, include navigation, and clean up unused elements

- Add `.quiz-topbar` with fixed positioning and spacing in `quiz.scss`
- Update `base.html.twig` to include `quiz/nav.html.twig` in a new `nav` block
- Remove unused "Manage Quiz" button from `select_season.html.twig`

* Refactor generateTemplate to reuse quizToXlsx and add second example question

- generateTemplate now builds an in-memory Quiz entity and delegates to
  quizToXlsx, eliminating duplicate spreadsheet-building logic
- Adds a second example question "Wie is de mol?" with 10 Dutch names
  (5 male, 5 female) to better illustrate the import format
- Updates tests to assert both example questions and adds a test for the
  blank-row halt behaviour in fillQuizFromArray (achieving 100% coverage)

* Move PHPUnit cache to /tmp to avoid writing into the mounted volume

* Update src/Service/QuizSpreadsheetService.php

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

assets/styles/backoffice.scss

@@ -0,0 +1,3 @@
+.col-result-xs { width: 10%; }
+.col-result-sm { width: 15%; }
+.col-result-md { width: 20%; }

assets/styles/quiz.scss

@@ -1,14 +1,97 @@
-html, body {
+html {
     height: 100%;
     background-image: url("../img/background.png");
-    background-position: center center;
+    background-position: center;
     background-repeat: no-repeat;
     background-color: black;
     color: white;
-
     display: grid;
     align-items: center;
-    justify-self: center;
+}
+
+body {
+    height: 100%;
+    background-image: url("../img/background.png");
+    background-position: center;
+    background-repeat: no-repeat;
+    background-color: black;
+    display: grid;
+    align-content: center;
+}
+
+.quiz-form-narrow {
+    max-width: 320px;
+    width: 100%;
+    margin: 0 auto;
+}
+
+.quiz-content {
+    width: fit-content;
+    max-width: min(760px, 100%);
+    margin: 0 auto;
+}
+
+.quiz-answers-grid {
+    display: grid;
+    grid-template-columns: repeat(2, auto);
+    column-gap: 2rem;
+
+    @media (max-width: 767px) {
+        grid-template-columns: 1fr;
+    }
+}
+
+.answer-btn {
+    display: flex;
+    align-items: center;
+    gap: 0.8rem;
+    background: transparent;
+    border: none;
+    color: white;
+    font-size: 1.1rem;
+    padding: 0.4rem 0;
+    cursor: pointer;
+    text-align: left;
+    line-height: 1.3;
+
+    &::before {
+        content: '';
+        display: block;
+        flex-shrink: 0;
+        width: 2rem;
+        height: 2rem;
+        background: radial-gradient(ellipse at 35% 30%, #6abf4b, #2d7a1f);
+        border-radius: 4px;
+        box-shadow: inset 0 1px 2px rgba(255, 255, 255, 0.25), 0 2px 6px rgba(0, 0, 0, 0.6);
+    }
+
+    &:hover,
+    &:focus {
+        color: #7ed45a;
+        outline: none;
+
+        &::before {
+            background: radial-gradient(ellipse at 35% 30%, #86d45f, #3d9c2a);
+        }
+    }
+}
+
+input.btn-check:checked + label.answer-btn {
+    color: #7ed45a;
+
+    &::before {
+        background: radial-gradient(ellipse at 35% 30%, #86d45f, #3d9c2a);
+        box-shadow: 0 0 10px rgba(106, 191, 75, 0.7), inset 0 1px 2px rgba(255, 255, 255, 0.3);
+    }
+}
+
+.quiz-topbar {
+    position: fixed;
+    top: 1rem;
+    right: 1rem;
+    z-index: 1030;
+    display: flex;
+    gap: 0.5rem;
 }
 
 .elimination-screen {