fix(forms): keep PDF-form export from dropping values when the label has '*' (#1407)

parse_markdown_to_values — the read-back path for export-pdf, the export
preview, and prepare-signed-reply — matched the bold field label with [^*]+, so
it could not match a label containing '*' (the near-universal required-field
marker: "Email *", "State *", "Signature *"). The value then stayed empty, so
the exported PDF and the signed-reply attachment came out blank for that field
with no error — a whole form of required fields could export completely empty.

Match the label non-greedily (.+?) so '*' in labels is tolerated while still
splitting at the first ':**' / '**[', which also preserves a value that itself
contains ':**'.

Adds tests/test_form_markdown_roundtrip.py (render -> parse roundtrip): asterisk
text/choice/signature labels survive (fail before, pass after); plain labels and
colon-bearing values are unaffected.

Co-authored-by: NubsCarson <nubs@nubs.site>

src/pdf_form_doc.py

@@ -126,8 +126,13 @@ def _decode_name(enc: str) -> str:
     """Inverse of _encode_name."""
     import urllib.parse
     return urllib.parse.unquote(enc or "")
-_TEXT_VALUE_RE = re.compile(r'\*\*[^*]+:\*\*\s*(?P<value>.*)$')
-_CHOICE_VALUE_RE = re.compile(r'\*\*[^*]+\*\*\s*\[[^\]]*\]\s*:\s*(?P<value>.*)$')
+# Label segment is non-greedy (.+?) so labels containing '*' — the near-universal
+# required-field marker, e.g. "Email *" — are tolerated, while still splitting at
+# the FIRST ':**' / '**[' so a value that itself contains ':**' is preserved.
+# (The old [^*]+ refused to match any label with an asterisk and silently
+# dropped that field's value on export.)
+_TEXT_VALUE_RE = re.compile(r'\*\*.+?:\*\*\s*(?P<value>.*)$')
+_CHOICE_VALUE_RE = re.compile(r'\*\*.+?\*\*\s*\[[^\]]*\]\s*:\s*(?P<value>.*)$')
 _CHECKBOX_VALUE_RE = re.compile(r'^\s*\[(?P<state>[xX ])\]')
 
 _PLACEHOLDERS = {"_(empty)_", "_(not selected)_", "_(empty)_.", "_(unsigned)_"}