Fix radon complexity warnings across browser table-view code + tests

[ajslater]

Summary

All five files reported by bin/lint-complexity.sh (radon cc --min C plus the mi --min B for test_browser_table_response.py) are now under threshold. Pure decomposition / consolidation — no behavior change.

What changed

Production code

Function	CC before	CC after	Change
intersections._compute_simple_m2m_intersections_batched	12	6	Extracted _initialize_simple_m2m_buckets, _union_simple_m2m_queries, _collect_simple_m2m_intersections. Main function reads as a 6-line pipeline.
order_by.BrowserOrderByView._add_comic_order_by	11	1	Split into _normalize_comic_order_key (key resolution) and _comic_order_fields_head / _comic_sort_name_head / _comic_indexed_head (head-building branches). Top-level method is a 2-line orchestrator.
annotate.order.BrowserAnnotateOrderView.annotate_extra_order_values	11	6	Hoisted the early-return predicate into _should_annotate_extras and the per-extra annotation map into _build_extra_annotations.

Tests

Function	CC before	CC after	Change
test_save_view_round_trips_table_fields	11	4	Extracted _save_named_view and _load_saved_settings round-trip helpers; collapsed four field-by-field assertions into a single dict-equality check against the live patch payload.
test_table_view_m2m_sort_groups_identical_sets	19	5	Extracted _create_sibling_comic factory (replaces three ~12-line Comic.objects.create blocks) and _assert_genre_sort_classes. The equivalence-class assertion uses frozenset + sorted for a single equality check.
test_table_view_simple_m2m_intersections_share_one_union_query	11	5	Extracted the seven-table or chain into a module-level _SIMPLE_M2M_THROUGH_TABLES tuple + a _count_through_table_queries helper that uses any().

File-level MI

• tests/test_browser_table_response.py: B (17.08) → A (19.66). Driven entirely by the function-level fixes above; no other restructuring.

Test plan

• bin/lint-complexity.sh clean (no functions over CC 10, no files at MI grade B)
• complexipy clean (no functions over CC 15)
• ruff check clean
• 193 backend pytest tests pass

Reviewer notes

• The new _create_sibling_comic test helper is private to the test class and replicates the setUp Comic-creation shape with a uniform size = 42 + issue_number formula. Per-call size keeps cumulative-sum assertions in adjacent tests deterministic. (Existing tests didn't use the helper because their assertions don't constrain size in ways that conflict with the formula — but if a future test does, override locally.)

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