chore: scope ruff ignores to tests, Qt and engineering notation

RUF001-003 are ignored repo-wide: × / ≈ / ² are deliberate in the
engineering docs and formulas, which also makes the scattered inline
noqa suppressions redundant. Tests use engineering symbols (A, I, L, E),
`importorskip` before imports and capitalised test names; Qt requires
camelCase signal names and PascalCase event overrides; OpenSees material
fields (cR1, epsU) mirror the solver verbatim. N806 stays exempt only for
the numeric modules that use L / Iz / Iy as symbols.

pyproject.toml

@@ -89,7 +89,25 @@ select = [
     "SIM",      # simplify
     "RUF",      # ruff-specific
 ]
-ignore = ["E501"]  # line length handled by formatter
+ignore = [
+    "E501",    # line-length handled by the formatter
+    "RUF001",  # ambiguous unicode: engineering notation (×, ≈, ²) is deliberate
+    "RUF002",
+    "RUF003",
+]
+
+[tool.ruff.lint.per-file-ignores]
+# Engineering symbols (A, I, L, E, P) and `importorskip`-then-import blocks
+# are normal in tests.
+"tests/**" = ["E402", "E741", "N802", "N806", "N815"]
+# Qt requires camelCase signal names and PascalCase event overrides.
+"src/otko/views/**" = ["N802", "N815"]
+"src/otko/viewmodels/**" = ["N815"]
+# Material fields mirror the OpenSees parameter names verbatim (cR1, epsU, ...).
+"src/otko/core/materials/__init__.py" = ["N815"]
+# Engineering symbols in numeric code: L (length), Iz/Iy (second moments).
+"src/otko/services/section_properties.py" = ["N806"]
+"src/otko/views/canvas3d/model_renderer.py" = ["N802", "N806", "N815"]
 
 [tool.ruff.format]
 quote-style = "double"