feat(chunks): rilevamento universale has_math/has_table + dollarmath plugin

- parser.py: integra dollarmath_plugin (graceful fallback) — blocchi $$…$$ → token math_block atomico
- segmenter.py: gestisce math_block → Block(kind=math, atomic=True, plain_text=[formula])
- packer.py: has_table rileva anche <table> in blocchi html; has_math rileva $$ e \begin{ nel contenuto
- +11 test (parser×3, segmenter×3, packer×5) — totale 65 test

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

chunks/packer.py

@@ -41,9 +41,18 @@ def _build_chunk(blocks: list[Block], index: int, config: ChunkerConfig,
         header_path=header_path,
         block_ids=[b.id for b in blocks],
         flags={
-            "has_code":    any(b.kind == "code"  for b in blocks),
-            "has_table":   any(b.kind == "table" for b in blocks),
-            "has_math":    any(b.kind == "math"  for b in blocks),
+            "has_code":    any(b.kind == "code" for b in blocks),
+            "has_table":   any(
+                b.kind == "table"
+                or (b.kind == "html" and "<table" in b.content.lower())
+                for b in blocks
+            ),
+            "has_math":    any(
+                b.kind == "math"
+                or "$$" in b.content
+                or r"\begin{" in b.content
+                for b in blocks
+            ),
             "is_overflow": total_chars > config.max_chars,
             "is_sparse":   total_chars < config.min_chars,
         },