fix(#1983): don't treat alternation-shaped class_start group 2 as a lineage parent

[squid-protocol]

Closes #1983.

Problem

detector.py's THE LINEAGE EXTRACTOR swept every class_start
match's group-2 capture into extracted_parents (→ the file's
parent_entity metadata) whenever the pattern had 2+ groups:

if rule_name == "class_start" and pattern.groups >= 2:
    extracted_parents.extend(m.group(2).strip() for m in matches if m.group(2))

Correct for class Foo extends Bar (g1 = name, g2 = parent). Wrong for
alternation-shaped class_start rules, where the name lands in group 1
or group 2 depending on which branch fired — never both:

lang	rule shape	broken result
fortran	(?:MODULE|INTERFACE|SUBMODULE)\s+(g1) | TYPE\s+(g2)	TYPE point → parent_entity = "point" (its own name)
dockerfile	FROM .. AS (g1) | FROM (g2)	bare FROM debian → parent_entity = "debian:…"
lua, abap	same alternation shape	same

The named-class path (_resolve_class_start_match) already handles this
correctly — it treats group 2 as inheritance only if name_group_idx == 1.
The lineage extractor just never got the same guard.

Fix

extracted_parents.extend(m.group(2).strip() for m in matches if m.group(2) and m.group(1))

Group 2 is a lineage parent only when group 1 (the name) also matched —
the same rule _resolve_class_start_match uses, so the two can't drift.
Class extraction itself is untouched; this only fixes the secondary
parent_entity field.

Verification

• New test_detector_lineage_ignores_alternation_shaped_class_start
  (fortran-shaped MODULE｜TYPE rule); existing
  test_detector_harvest_above_and_lineage (name-then-parent) still passes.
• crucible_check.py --update: 5 Parent Entity fields removed, nothing
  else — 2 fortran files (TYPE names), 3 dockerfile files (bare FROM
  base images, including the syscall.Dockerfile case cited in the issue).
  No class-count or other structural drift. Both golden masters re-blessed.
• tri_comparison_chart.py --all --ci: all OK, no precision regressions.
• ruff / mypy / dead-key / ast-accuracy clean.

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