Polish editors, previews, persistence and docs

Cross-platform refinements to appearance/battery/charger editors, tabs
and navigation, plus persistence, screenshot previews and CLAUDE.md docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -2,6 +2,15 @@
 
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
+## Two apps in this repo
+
+- **iOS** (`Cable/`) — SwiftUI + SwiftData. **This document describes the iOS app unless stated otherwise.**
+- **Android** (`android/`) — a native Kotlin/Jetpack Compose port that mirrors every iOS feature (package root `app.voltplan.cable`, Room persistence, same Aptabase analytics). See **`android/README.md`** for its architecture and build instructions before working on it.
+
+Behavior and data shape are meant to stay in sync across both — when changing a user-facing feature on one platform, check the other. See [Export Options](#export-options) for one such cross-platform contract.
+
+**Apply every instruction to both the iOS and Android versions unless explicitly told otherwise.** Any feature, fix, or change requested without naming a platform must land on both apps and stay behaviorally in sync.
+
 ## Build & Test Commands
 
 Use the **Xcode MCP server** tools instead of `xcodebuild` CLI:
@@ -106,13 +115,25 @@ All list views use consistent styling:
 - Use `String(localized:defaultValue:)` — **not** `NSLocalizedString`. The `defaultValue` serves as English fallback and avoids showing raw keys when a Localizable.strings entry is missing.
 - When adding new user-facing strings, add translations to **all 5** Localizable.strings files immediately.
 
-## PDF Export Pattern
+## Export Options
+
+Three export options, available from the Overview tab's share menu plus the BOM sheet. **Keep iOS and Android (`android/.../pdf/`) in sync — they must offer the same exports.**
+
+1. **System Overview (PDF)** — summary + a full-page wiring diagram + per-entity tables.
+2. **Bill of Materials (PDF)** — categorized component list.
+3. **Wiring Diagram (PNG)** — standalone diagram image.
+
+The wiring diagram (used both as the standalone PNG and the Overview PDF's diagram page) is fetched from the shared **VoltPlan diagram API** (`POST https://voltplan.app/api/diagram/generate`, JSON payload of system/loads/batteries/chargers, returns PNG). Both platforms send the identical payload shape; falls back gracefully when the API is unreachable (iOS draws a Core Graphics diagram; Android omits the PDF page / shows an error toast for the standalone export).
+
+### PDF Export Pattern (iOS)
 
 PDF exports use `UIGraphicsPDFRenderer` with A4 portrait format. The pattern is:
 - **Exporter struct** (e.g. `SystemOverviewPDFExporter`, `SystemBillOfMaterialsPDFExporter`) with snapshot data types — keeps Core Graphics rendering isolated from SwiftUI/SwiftData.
 - **ShareSheet** triggered via `@State` item binding in the parent view.
 - **Toolbar button** (not inline content) for the export action.
 
+On Android the equivalents live in `android/app/src/main/java/app/voltplan/cable/pdf/`: `SystemOverviewPdf`, `SystemBomPdf`, `SystemDiagram` (diagram fetch + PNG export), and `PdfShare` (`PdfDocument` + `FileProvider`/`ACTION_SEND`).
+
 ## Screenshots
 
 App Store screenshots are generated via XCUITests running on simulators, automated by `shooter.sh`.