feat: v0.3.0 re-release - add dashboard & sessions, hide pi option

- Usage dashboard: KPIs, model split, daily bars, year heatmap, recent requests
- Sessions management: list/preview/archive/delete with streaming preview
- Double-click daily bar opens per-model breakdown modal
- Paginated recent requests (30/page)
- Hide pi option from nav (kept code, just removed from UI)
- Timezone fixes: today/day_key/heatmap now use local calendar day
- Streaming preview with 20MB byte cap + 500-char frontend clip
- README attribution to kimicode-dashboard (MIT, JochenYang)

src-tauri/Cargo.toml

@@ -15,8 +15,11 @@ tauri-plugin-single-instance = "2.0.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 indexmap = { version = "2.2", features = ["serde"] }
-chrono = "0.4"
+chrono = { version = "0.4", features = ["serde"] }
 anyhow = "1.0"
+regex = "1"
+walkdir = "2"
+fs_extra = "1"
 reqwest = { version = "0.12", features = ["json", "rustls-tls"], default-features = false }
 dirs = "5.0"
 toml = "0.8"