Fix quoted MIME-DIR parameter parsing

Correct the vCard 3 parameter parser so quoted parameter values are
consumed according to the MIME-DIR grammar instead of failing
immediately on the opening double quote.

The fix explicitly advances past the opening quote, reads the quoted
qsafe-char sequence, and strips the surrounding quotes from the returned
parameter value. Unquoted parameter handling is unchanged.

Add private parser coverage for quoted parameter values and quoted
values containing commas, plus a public regression test showing that
quoted LANGUAGE and TYPE parameters are accepted by the vCard 3 parser.

AI-Assisted: yes
AI-Tool: OpenAI Codex / gpt-5.4 xhigh

src/vcard/vcard3.nim

@@ -902,11 +902,12 @@ proc readParamValue(p: var VCardParser): string =
   ## Read a single parameter value at the current read position or error.
   p.setBookmark
   if p.peek == '"':
+    discard p.read
     while QSAFE_CHARS.contains(p.peek): discard p.read
     if p.read != '"':
       p.error("quoted parameter value expected to end with a " &
         "double quote (\")")
-    result = p.readSinceBookmark[0 ..< ^1]
+    result = p.readSinceBookmark[1 ..< ^1]
   else:
     while SAFE_CHARS.contains(p.peek): discard p.read
     result = p.readSinceBookmark
@@ -1393,6 +1394,24 @@ proc runVCard3PrivateTests*() =
     assert p.read == '='
     assert p.readParamValue == "Fun&Games%"
 
+  # "readParamValue quoted":
+  block:
+    var p = initParser("FN;LANGUAGE=\"en\":John Smith")
+    assert p.readName == "FN"
+    assert p.read == ';'
+    assert p.readName == "LANGUAGE"
+    assert p.read == '='
+    assert p.readParamValue == "en"
+
+  # "readParamValue quoted with comma":
+  block:
+    var p = initParser("LABEL;TYPE=\"HOME,POSTAL\":123 Main St.")
+    assert p.readName == "LABEL"
+    assert p.read == ';'
+    assert p.readName == "TYPE"
+    assert p.read == '='
+    assert p.readParamValue == "HOME,POSTAL"
+
   # "readParams":
   block:
     var p = initParser("TEL;TYPE=WORK;TYPE=Fun&Games%,Extra:+15551234567")
@@ -1407,6 +1426,15 @@ proc runVCard3PrivateTests*() =
     assert params[1].values[0] == "Fun&Games%"
     assert params[1].values[1] == "Extra"
 
+  # "readParams quoted":
+  block:
+    var p = initParser("FN;LANGUAGE=\"en\":John Smith")
+    assert p.readName == "FN"
+    let params = p.readParams
+    assert params.len == 1
+    assert params[0].name == "LANGUAGE"
+    assert params[0].values == @["en"]
+
   # "readValue":
   block:
     var p = initParser("TEL;TYPE=WORK:+15551234567\r\nFN:John Smith\r\n")