Add URL preload feature and live example CTAs on reference pages

- App: parse ?xslt=, ?xml=, ?version=, ?title= query params on load
  (base64url-encoded) to pre-populate the editor from external links
- App: Share button in XSLT toolbar generates a preload URL for the
  current tab and copies it to clipboard (icon flips to ✓ for 2s)
- Icon: add share and check icons
- Blog: 225 reference pages now include a tryUrl frontmatter field
  with the first example pre-encoded; layout renders "Open live
  example in XSLT Playground →" CTA pointing directly to that URL
- Script: scripts/add_try_urls.py to regenerate tryUrl fields

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/add_try_urls.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+"""
+Reads all /xslt/functions/*.md pages, extracts the first XSLT + XML example,
+and adds a `tryUrl` field to the frontmatter that links directly to xsltplayground.com
+with the example pre-loaded via base64url query params.
+"""
+import os
+import re
+import base64
+
+FUNCTIONS_DIR = os.path.join(
+    os.path.dirname(__file__),
+    "..", "site", "content", "xslt", "functions"
+)
+BASE_URL = "https://xsltplayground.com/"
+FALLBACK_XML = '<?xml version="1.0" encoding="UTF-8"?>\n<root/>'
+
+
+def b64url(s: str) -> str:
+    return base64.urlsafe_b64encode(s.encode("utf-8")).rstrip(b"=").decode("ascii")
+
+
+def extract_block(content: str, label: str) -> str | None:
+    pattern = rf"\*\*{re.escape(label)}:\*\*\s*```xml\s*\n(.*?)\n```"
+    m = re.search(pattern, content, re.DOTALL)
+    return m.group(1).strip() if m else None
+
+
+def process_file(filepath: str) -> str:
+    with open(filepath, encoding="utf-8") as f:
+        text = f.read()
+
+    # Match YAML frontmatter block
+    fm_match = re.match(r"^---\n(.*?)\n---\n", text, re.DOTALL)
+    if not fm_match:
+        return "no-frontmatter"
+
+    fm_text = fm_match.group(1)
+    if "tryUrl:" in fm_text:
+        return "already-set"
+
+    # Extract version from frontmatter
+    version_m = re.search(r'^version:\s*["\']?([^"\'\n]+)["\']?', fm_text, re.MULTILINE)
+    version = version_m.group(1).strip() if version_m else "1.0"
+
+    content = text[fm_match.end():]
+
+    xslt = extract_block(content, "Stylesheet")
+    xml = extract_block(content, "Input XML")
+
+    if not xslt:
+        return "no-xslt"
+
+    if not xml:
+        xml = FALLBACK_XML
+
+    url = f"{BASE_URL}?xslt={b64url(xslt)}&xml={b64url(xml)}&version={version}"
+
+    # Insert tryUrl before the closing --- of the frontmatter
+    insert_pos = fm_match.end() - 4  # points to start of closing ---\n
+    new_text = text[:insert_pos] + f'tryUrl: "{url}"\n' + text[insert_pos:]
+
+    with open(filepath, "w", encoding="utf-8") as f:
+        f.write(new_text)
+
+    return "ok"
+
+
+def main():
+    functions_dir = os.path.abspath(FUNCTIONS_DIR)
+    files = [
+        f for f in os.listdir(functions_dir)
+        if f.endswith(".md") and f != "_index.md"
+    ]
+
+    counts = {"ok": 0, "already-set": 0, "no-xslt": 0, "no-frontmatter": 0, "error": 0}
+
+    for fname in sorted(files):
+        fpath = os.path.join(functions_dir, fname)
+        try:
+            result = process_file(fpath)
+            counts[result] = counts.get(result, 0) + 1
+            if result not in ("ok", "already-set"):
+                print(f"  SKIP [{result}] {fname}")
+        except Exception as e:
+            counts["error"] += 1
+            print(f"  ERROR {fname}: {e}")
+
+    print(f"\nDone: {counts['ok']} updated, {counts['already-set']} already had tryUrl, "
+          f"{counts['no-xslt']} skipped (no stylesheet found), {counts['error']} errors")
+
+
+if __name__ == "__main__":
+    main()