feat(view): round bar bends at the centre-line radius; bend factors as inputs on ③

Bars drawn through several points are one tube each, with every bend rounded by R·tan(φ/2) at the centre-line radius
(inner factor × d + d/2). The inside-radius factors (D16 and below, D19–D25, D29–D35, D38 and above) are inputs in 공통
설정, with KDS-based defaults 2 / 3 / 4 / 5. The size-class limits sit in one place (SIZE_CLASS), which also fixes
D25 (25.4) being read as the D29–D35 class in hookLength. The helper bendDeduction gives the centre-line deduction for
the length option, which is not yet applied to the 철근표 lengths.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

tests/project.test.ts

@@ -68,8 +68,8 @@ describe('project file round trip (spec §8, plan B3)', () => {
 describe('③ 공통 설정 in the project file', () => {
   it('fck and fy are kept through save and open; older files get the defaults through the app', () => {
     const p = sampleProject();
-    const withCommon = { ...p, common: { fck: 35, grade: { D: 300, H: 400, S: 500 } } };
-    expect(parseProject(serializeProject(withCommon)).common).toEqual({ fck: 35, grade: { D: 300, H: 400, S: 500 } });
+    const withCommon = { ...p, common: { fck: 35, grade: { D: 300, H: 400, S: 500 }, bend: { small16: 2, main25: 3, main35: 4, main51: 5 } } };
+    expect(parseProject(serializeProject(withCommon)).common).toEqual(withCommon.common);
     expect(parseProject(serializeProject(p)).common).toBeUndefined();
   });
 });