Give jetc a dedicated, fully inert <comment> handler at compile time

<comment> had no special-case in jetc's compiler at all - it fell
through to parseFallback(), the generic unknown-tag path, which hunts
for a tag's own closing tag via scanBody()/skipQuotedValue(), the same
quote-aware, backslash-escape-interpreting scanning real Jet attribute
syntax needs. A comment containing an explanatory " sequence (a JSON
example in prose, say) or a literal <else>/<if>-looking word - both
already confirmed, separately, to corrupt jetc when they turn up
inside a JS // comment - hit the exact same corruption here too, just
triggered from inside a <comment> block instead.

Added skipCommentTag(), which only tracks same-tag-name nesting depth
via the existing case-insensitive matchTagOpen/matchTagClose and
otherwise ignores every character - no quote tracking, no other-tag
recognition, nothing a comment's own body could ever trip over. Wired
into parseNodes() alongside the other recognized top-level tags;
unlike those, it pushes no node at all; the comment contributes
nothing to the compiled output, matching the runtime interpreters own
__comment behavior but now safe at compile time too.

Verified directly: a scratch .jet with five <comment> blocks (plain,
a bare quote, a backslash-quote JSON example, literal <else>/<if>
text, and nested comments with their own quotes) all compiled clean
and left zero trace in the generated code, with the <if> immediately
following them compiling correctly too - confirming nothing after a
tricky comment gets corrupted either.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

jetc/JetParser.h

@@ -61,6 +61,15 @@ namespace jetc {
       void skipQuotedValue(size_t &p);
       void skipEmbeddedTag(size_t &p);
 
+      // <comment>...</comment> must be fully inert regardless of what's
+      // inside it - unlike the generic parseFallback/scanBody path this
+      // tag used to fall through to (which applies the same quote/
+      // backslash-escape and nested-tag scanning real Jet syntax needs),
+      // this tracks only same-tag-name nesting depth via matchTagOpen/
+      // matchTagClose and otherwise ignores every character. See its own
+      // definition for the quote-corruption bug this specifically closes.
+      void skipCommentTag(size_t &p);
+
       std::map<std::string, std::string> parseAttrs(bool &hasContainer);
 
       // Scans forward from bodyStart (just after the opening tag's '>') for