feat(cms): U2 render content/ into detail pages (characterization-verified)

Add tools/build_content.py: renders every content/ entry into its blog /
news / event detail page by self-templating the page's own chrome and
replacing only content-derived regions (title, article header, hero,
body, and — for new pages only — the scrollspy).

Faithful reproduction, proven against the live site:
- body_format: html fragments injected verbatim, so guide-boxes, inline
  figures and event galleries render unchanged.
- scrollspy sidebars are preserved (labels are hand-curated, shorter than
  the H2s); only generated when a page has none.
- <title> suffix derived per page, so EN/SI " - MSOS", MK " - МСОС", and
  suffix-less event titles all reproduce exactly.
- hero /images/… rewritten to the page's ../../../ depth.
- ASCII-only console output (no cp1252 crash on Windows/CI).

tools/tests/test_build_content.py: 8 characterization tests; the core one
renders all 51 pages and asserts each is semantically equivalent
(whitespace/attr-order-insensitive) to the current page — the R5
no-regression guarantee.

Does NOT overwrite the committed pages; whether generated pages are
committed vs built fresh in CI is decided in U4/U5. Run:
  python tools/build_content.py --check   # verify equivalence
  python tools/build_content.py --write    # emit pages (for U4)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/tests/test_build_content.py

@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+"""
+Characterization tests for tools/build_content.py (U2).
+
+The core guarantee (plan R5): rendering every content/ entry reproduces the
+CURRENT live detail page, compared semantically (whitespace- and
+attribute-order-insensitive). This is what protects against SEO/layout
+regressions when the build takes over page generation.
+
+Run directly:   python tools/tests/test_build_content.py
+Or with pytest: pytest tools/tests/test_build_content.py
+"""
+import os
+import sys
+import unittest
+
+TOOLS = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+ROOT = os.path.dirname(TOOLS)
+sys.path.insert(0, TOOLS)
+
+import build_content as bc  # noqa: E402
+
+
+def _render(out_rel):
+    """Render the content entry whose output path ends with out_rel."""
+    for meta, body, _path in bc.iter_entries():
+        if bc.output_path(meta).replace(os.sep, "/").endswith(out_rel):
+            base = bc._template_html(meta)
+            return meta, bc.build_entry(meta, body, base)
+    raise AssertionError(f"no content entry maps to {out_rel}")
+
+
+def _current(out_rel):
+    with open(os.path.join(ROOT, out_rel), encoding="utf-8") as f:
+        return f.read()
+
+
+class ReproducesEverySite(unittest.TestCase):
+    def test_all_pages_semantically_equivalent(self):
+        """Every rendered page must equal the current page (semantic compare)."""
+        _built, mismatches = bc.run(check=True, write=False)
+        self.assertEqual(mismatches, [], f"pages diverged from the live site: {mismatches}")
+
+
+class TitleSuffixFaithful(unittest.TestCase):
+    def test_cyrillic_suffix_preserved(self):
+        # MK pages use ' - МСОС' (Cyrillic); it must survive, not be dropped.
+        meta, rendered = _render("mk/projects/macedonian-student-night-in-ljubljana/index.html")
+        self.assertIn("- МСОС</title>", rendered)  # - МСОС
+
+    def test_no_suffix_stays_absent(self):
+        # Some event pages have no ' - MSOS' suffix; we must not invent one.
+        _meta, rendered = _render("en/projects/morning-coffee-in-front-of-ctk/index.html")
+        self.assertNotIn("- MSOS</title>", rendered)
+
+
+class RichContentSurvives(unittest.TestCase):
+    def test_event_gallery_and_lightbox_render(self):
+        _meta, rendered = _render("en/projects/paint-and-wine-at-sunset/index.html")
+        self.assertIn("event-gallery", rendered)
+        self.assertIn("eg-thumb", rendered)
+
+    def test_blog_guidebox_and_scrollspy_render(self):
+        _meta, rendered = _render("en/blog/how-to-open-slovenian-bank-account/index.html")
+        self.assertIn("guide-box", rendered)
+        self.assertIn('class="scrollspy-nav"', rendered)
+
+
+class ScrollspyPreservesCuratedLabels(unittest.TestCase):
+    def test_hand_shortened_labels_not_overwritten(self):
+        # The body H2 is long; the sidebar label was shortened by hand. The
+        # rendered page must keep the curated short label, not the H2 text.
+        _meta, rendered = _render("en/projects/macedonian-student-night-in-ljubljana/index.html")
+        self.assertIn(">Idea to Movement</a>", rendered)
+
+
+class HeroPathDepth(unittest.TestCase):
+    def test_hero_src_uses_relative_depth(self):
+        _meta, rendered = _render("en/blog/how-to-open-slovenian-bank-account/index.html")
+        # Hero must resolve from the page's depth, not a root-absolute path.
+        self.assertIn('src="../../../images/', rendered)
+        self.assertNotIn('src="/images/', rendered)
+
+
+class NewsStructure(unittest.TestCase):
+    def test_news_uses_news_article_body(self):
+        _meta, rendered = _render("en/news/proof-of-means-updated-2026/index.html")
+        self.assertIn('class="news-article-body"', rendered)
+        self.assertIn('class="news-article-date"', rendered)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)