docs(pdftract-4brcu): Add verification note for list detection

All acceptance criteria verified PASS. Implementation already complete
in crates/pdftract-core/src/layout/list.rs with 20 passing tests.

notes/pdftract-4brcu.md

@@ -0,0 +1,74 @@
+# pdftract-4brcu: List Detection Implementation
+
+## Summary
+
+The list detection implementation was already complete in `crates/pdftract-core/src/layout/list.rs`. This task verified that the implementation meets all acceptance criteria.
+
+## Implementation Details
+
+### Location
+- File: `crates/pdftract-core/src/layout/list.rs`
+- Module: `pdftract_core::layout::list`
+- Exported via: `crates/pdftract-core/src/layout/mod.rs`
+
+### Key Functions
+
+1. **`classify_list<S, L>(block: &Block<S>) -> bool`**
+   - Returns `true` when ≥80% of block's lines start with bullet/numbered pattern
+   - Empty blocks return `false`
+
+2. **`starts_with_bullet(line_text: &str) -> bool`**
+   - Pattern: `^\s*[•‣◦⁃\-\*]\s`
+   - Matches Unicode bullets and ASCII marks
+
+3. **`starts_with_number(line_text: &str) -> bool`**
+   - Pattern: `^\s*\d+[.\)]\s`
+   - Matches "1.", "2)", etc.
+
+### Regex Patterns
+```rust
+BULLET_RE:    r"^\s*[•‣◦⁃\-\*]\s"
+NUMBER_RE:    r"^\s*\d+[.\)]\s"
+```
+
+## Acceptance Criteria Verification
+
+All acceptance criteria PASS:
+
+| # | Criterion | Test | Result |
+|---|-----------|------|--------|
+| 1 | 3 "* Item" lines → List | `test_classify_list_three_bullet_items` | PASS |
+| 2 | 3 "1. First/2. Second/3. Third" lines → List | `test_classify_list_three_numbered_items` | PASS |
+| 3 | 1 "* Solo" line → List | `test_classify_list_single_bullet_item` | PASS |
+| 4 | 4/5 "- " starts → List | `test_classify_list_four_of_five_bullet_items` | PASS |
+| 5 | 2/5 "- " starts → NOT List | `test_classify_list_two_of_five_bullet_items` | PASS |
+
+## Test Results
+
+```
+running 20 tests
+test layout::list::tests::test_classify_list_empty_block ... ok
+test layout::list::tests::test_classify_list_exactly_80_percent ... ok
+test layout::list::tests::test_classify_list_four_of_five_bullet_items ... ok
+test layout::list::tests::test_classify_list_just_below_80_percent ... ok
+test layout::list::tests::test_classify_list_mixed_bullet_and_numbered ... ok
+test layout::list::tests::test_classify_list_single_bullet_item ... ok
+test layout::list::tests::test_classify_list_three_bullet_items ... ok
+test layout::list::tests::test_classify_list_three_numbered_items ... ok
+test layout::list::tests::test_classify_list_two_of_five_bullet_items ... ok
+test layout::list::tests::test_classify_list_unicode_bullets ... ok
+test layout::list::tests::test_classify_list_zero_matching ... ok
+... (9 more helper tests for starts_with_bullet/starts_with_number)
+
+test result: ok. 20 passed; 0 failed
+```
+
+## Notes
+
+- Lettered (a., b.) and Roman (I., II.) lists are NOT covered in v0.1.0 (as per plan)
+- Indented sub-bullets (nesting) is deferred (as per plan)
+- Unicode bullets (•, ‣, ◦, ⁃) are matched as literal codepoints (per INV)
+
+## Git Status
+
+No file changes required - implementation was already complete and passing.