Fix complementary kp-wholepage panels: recover video organics, classify as knowledge

[gitronald]

Problem

On a complementary kp-wholepage panel (a music/entity panel that sits beside an intact organic column, not collapsing it), the 0.9.0a1 sub-column model misfired and the panel itself was mislabeled. Surfaced on this is my life billy joel youtube:

• The 10 YouTube video organics (div.g, organic-position siblings of the panel) were dropped — 0.9.0a0 emitted them as 10 general/video results, 0.9.0a1 emitted 0.
• The music panel was labeled searches_related / or_give_general_feedback instead of knowledge / panel.

Root causes & fixes

1. extractors/extractor_main.py — _kp_organics_outside (the gate regression). The complementary-panel guard only recognized organics containing div.tF2Cxc, so it missed video-style div.g organics (a YouTube div.g has h3 + a[href] but no tF2Cxc). The collapse gate misfired and the sub-column path discarded the video organics. Broadened the organic test to "titled link" (h3 + a[href]), restoring the invariant "no div.g organics in #rso outside the panel."

2. classifiers/main.py — ClassifyMainHeader.classify. Header-text classification runs before the structural knowledge_panel check, so the panel's inner "People also search for" sub-carousel heading made the whole panel classify as searches_related. The header classifier now defers for whole-page (kp-wholepage-osrp) panels, letting the structural classifiers (available_on, knowledge_panel) type them correctly. Scoped so it does not affect available_on panels (e.g. "watch the office", "where to watch breaking bad").

3. component_parsers/knowledge.py — _subtype_dynamic_section. For a whole-page entity panel the generic panel sub_type is correct; an internal subcard (a PASF carousel, or a feedback affordance whose heading precedes it) shouldn't define the panel's sub_type. Defers for kp-wholepage-osrp panels so the component stays knowledge / panel.

Result on 3917a73cbceb ("this is my life billy joel youtube")

10x general / video                     (recovered)
 1x knowledge / panel                   (was searches_related / or_give_general_feedback)
 1x searches_related / related_searches (footer)

12 results, 0 unknown — matches the 0.9.0a0 organic recovery with corrected panel typing.

Tests

• Added fixture 3917a73cbceb to tests/fixtures/serps.json.bz2 (86 -> 87) with a note documenting all three guards, plus its snapshot.
• Full suite: 336 passed, 4 skipped, 87 snapshots. No existing fixture changed; the true collapsed kp-wholepage case ("30 year mortgage rates") is unaffected.