Sprint 11/12/13 — 선택하이라이트 + 저장/로드 + Tauri앱 스켈레톤

Sprint 11 (Selection highlight + 단면 UI):
- FeatureDraw: CPU 정점 저장, update_highlight() — 선택 시 yellow-orange
- 렌더 루프: background mesh(지면+선형) + 피처별 독립 draw call 분리
- SceneParams: GirderSectionType (PscI / SteelBox), show_alignment
- egui: 단면형식 ComboBox, 선형표시 checkbox
- SteelBox 단면 지원 (span 비례 자동 치수)
- build_background_scene(): 지면+선형만 반환

Sprint 12 (Project save/load):
- project_file.rs: ProjectFile struct, to_params/from_params, save/load JSON
- egui: 💾 저장 / 📂 불러오기 버튼
- projects/ 폴더 자동 생성

Sprint 13 (Tauri app skeleton):
- crates/app/: Cargo.toml + main.rs (Tauri v2 통합 scaffold)
- 기동 시 PureRustKernel 동작 검증
- Tauri setup checklist 주석으로 문서화
- workspace에 cimery-app 추가

cargo check --workspace 통과

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cimery/crates/viewer/src/project_file.rs

@@ -0,0 +1,79 @@
+//! cimery project file — JSON save/load of SceneParams.
+//!
+//! Format: `cimery/projects/*.cimery.json`
+//! Sprint 12: SceneParams only. Sprint 13+: Feature IRs + Alignment.
+
+use serde::{Deserialize, Serialize};
+use super::bridge_scene::{GirderSectionType, SceneParams};
+
+// ─── Serialisable form of SceneParams ────────────────────────────────────────
+
+#[derive(Serialize, Deserialize)]
+struct SectionTypeStr(String);
+
+#[derive(Serialize, Deserialize)]
+pub struct ProjectFile {
+    pub version:        u32,
+    pub name:           String,
+    pub span_m:         f64,
+    pub girder_count:   usize,
+    pub girder_spacing: f32,
+    pub girder_height:  f32,
+    pub slab_thickness: f32,
+    pub section_type:   String,   // "psc_i" | "steel_box"
+    pub show_alignment: bool,
+}
+
+impl ProjectFile {
+    pub fn from_params(name: &str, p: &SceneParams) -> Self {
+        Self {
+            version:        1,
+            name:           name.to_owned(),
+            span_m:         p.span_m,
+            girder_count:   p.girder_count,
+            girder_spacing: p.girder_spacing,
+            girder_height:  p.girder_height,
+            slab_thickness: p.slab_thickness,
+            section_type:   match p.section_type {
+                GirderSectionType::PscI     => "psc_i".into(),
+                GirderSectionType::SteelBox => "steel_box".into(),
+            },
+            show_alignment: p.show_alignment,
+        }
+    }
+
+    pub fn to_params(&self) -> SceneParams {
+        SceneParams {
+            span_m:         self.span_m,
+            girder_count:   self.girder_count,
+            girder_spacing: self.girder_spacing,
+            girder_height:  self.girder_height,
+            slab_thickness: self.slab_thickness,
+            section_type:   match self.section_type.as_str() {
+                "steel_box" => GirderSectionType::SteelBox,
+                _           => GirderSectionType::PscI,
+            },
+            show_alignment: self.show_alignment,
+        }
+    }
+
+    pub fn save(&self, path: &std::path::Path) -> std::io::Result<()> {
+        let json = serde_json::to_string_pretty(self)
+            .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?;
+        std::fs::write(path, json)
+    }
+
+    pub fn load(path: &std::path::Path) -> std::io::Result<Self> {
+        let json = std::fs::read_to_string(path)?;
+        serde_json::from_str(&json)
+            .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))
+    }
+}
+
+/// Default project save path (relative to cimery workspace root).
+pub fn default_save_path(name: &str) -> std::path::PathBuf {
+    let mut p = std::path::PathBuf::from("projects");
+    std::fs::create_dir_all(&p).ok();
+    p.push(format!("{}.cimery.json", name));
+    p
+}