docs: add SCENARIO/SECTION patterns to technical reference

docs/technical_reference.md

@@ -297,6 +297,14 @@ SCENARIO tests group related assertions under SECTION sub-tests. Each SECTION is
 
 In `--list-tests` output, SCENARIO tests display with "Scenario: " prefix. When filtering by name, wildcards handle the prefix transparently.
 
+#### SCENARIO/SECTION Patterns
+- Setup between SCENARIO and SECTIONs = fixture (runs once per SECTION)
+- Use lambdas that capture the fixture to eliminate repeated setup
+- Reuse structs in-place (mutate fields) rather than recreating
+- Single-line sections are valid: `SECTION("name") { helper(arg); }`
+- One SECTION per test is fine — SCENARIO provides grouping + fixture scope
+- `using Catch::Matchers::WithinAbs;` after all includes
+
 Use `WithinAbs(expected, tolerance)` for floating-point comparisons (NOT `Approx()`).
 
 ## Hybrid Documentation Strategy