fix: 7 regex bugs from IHK Konstanz ground truth analysis

Fixes based on manual verification of all 30 failed checks:
1. Cookie table: recognize "folgende cookies" + column headers as text
2. Cookie names: add JSESSIONID, cookieinfo, et_id, BT_* patterns
3. Essential justified: match "sitzung zuordnen", "betrieb der website"
4. Social bookmarks: recognize as 2-click alternative
5. DSFA plural: "kanaelen" now matches alongside "kanal"
6. Section splitter: skip-headings no longer lose subsequent text
   (Risikoabwaegung section was cut from DSFA, losing risk scores)
7. Cookie legal basis: accept Art. 6(1)(f) in cookie context

Reduces false positives from 7 to ~1-2 for IHK Konstanz test case.
Ground truth table: zeroclaw/docs/ground-truth-ihk-konstanz.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/api/agent_doc_check_routes.py

@@ -303,7 +303,11 @@ def _split_into_sections(text: str, parent_label: str, url: str) -> list[dict]:
             and stripped[0].isupper()
         )
 
-        if is_heading and current_heading and len("\n".join(current_text)) > 200:
+        # Skip-headings should NOT start a new section — their text
+        # belongs to the previous section (e.g. "Risikoabwägung" inside DSFA)
+        is_skip = is_heading and stripped.lower().strip() in SKIP_HEADINGS
+
+        if is_heading and not is_skip and current_heading and len("\n".join(current_text)) > 200:
             # Save previous section
             sec_text = "\n".join(current_text)
             sec_type = _classify_section(current_heading)
@@ -315,7 +319,7 @@ def _split_into_sections(text: str, parent_label: str, url: str) -> list[dict]:
                     "word_count": len(sec_text.split()),
                 })
 
-        if is_heading:
+        if is_heading and not is_skip:
             current_heading = stripped
             current_text = []
         else: