Migrate Electron app from JavaScript to TypeScript

[Copilot]

Adds TypeScript tooling and migrates main process and core utility modules to provide type safety for IPC boundaries, Electron APIs, and image processing operations.

Changes

Tooling & Build

• Added TypeScript compiler with allowJs: true for incremental migration
• Configured output to dist/, updated main entry point and Electron Builder config
• Removed outdated @types/electron@1.4.38, using Electron 37's built-in types instead

Type Definitions

• Centralized IPC channel names and payload types in types/ipc.ts
• Defined type-safe interfaces for context menus, dialogs, and layer events

File Migrations (JS → TS)

• main.ts: Typed Electron APIs (IpcMainEvent, BrowserWindow, MenuItemConstructorOptions)
• core/pix.ts: Typed PIX format with Sharp library interfaces, fixed channels type constraint
• utils/ipc_bridge.ts: Generic IPC forwarder with typed handlers
• features/image_mode.ts: Converted to enum with typed mode manager class

Key Technical Details

// Before: untyped dialog calls
dialog.showOpenDialog(...).then(result => {
  event.sender.send("openImgCMD", result.filePaths);
});

// After: typed with proper async/await
const result = await dialog.showOpenDialog({...});
if (!result.canceled) {
  event.sender.send("openImgCMD", result.filePaths);
}

Sharp library type fix:

// Channels must be union type, not number
raw: { width, height, channels: channels as 1 | 2 | 3 | 4 }

All TypeScript files compile to CommonJS in dist/ maintaining compatibility with existing JS modules. Remaining files continue to work via allowJs: true and can be migrated incrementally.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Migration to typescript</issue_title>
<issue_description>Summary

Migrate Pegasus Electron app from JavaScript to TypeScript incrementally to improve type safety, DX, and maintainability while minimizing disruption.
Motivation

Strong typing for IPC contracts and render/main boundaries.
Catch runtime errors earlier; safer refactors as features grow.
Improve discoverability with IDE tooling and types.
Scope

Add TypeScript toolchain and config.
Compile to dist and point Electron to compiled outputs.
Incremental file-by-file migration with allowJs.
Provide type definitions for Electron, Node, and frequently used libs.
Keep current security model (no preload refactor yet).
Out of Scope

Security model changes (e.g., contextIsolation: true, preload API).
Large architectural changes or bundler switch.
Test framework introduction.
Plan

Phase 1: Tooling + Build
Phase 2: Type-safe IPC contracts
Phase 3: Core + Utils migration
Phase 4: Main/Renderer migration per panel
Phase 5: Strict mode tightening and cleanup
Tasks

Tooling
Add TypeScript: npm i -D typescript @types/node @types/electron
Add tsconfig.json with outDir: dist, rootDir aligned to repo, allowJs: true, resolveJsonModule: true.
Update package.json:
main → dist/main.js
Scripts: build:ts, watch:ts, dev (tsc watch + electron)
Build Pathing
Ensure assets and pages resolve correctly from compiled output.
Verify Electron Builder targets use compiled dist/main.js.
IPC Types
Centralize IPC channel names in a shared type module (e.g., types/ipc.ts).
Type IPCBridge methods and payloads.
Incremental Migration
Core: pix.js → core/pix.ts, image_layer.js → image_layer.ts, image_renderer.js → image_renderer.ts
Utils: ipc_bridge.js → utils/ipc_bridge.ts
Features: image_mode.js → features/image_mode.ts (enum + class typing)
Processing: image_processor.js → processing/image_processor.ts (define image buffers/types)
Main: main.js → main.ts (Electron types, IPC handlers)
Renderer: renderer/*.js per panel → .ts (DOM and IPC typing)
Config Tweaks
Add paths aliases if needed; ensure relative imports still resolve after build.
Add ESLint with TS plugin optionally for consistency.
CI/Build
Ensure CI runs npm run build:ts before packaging.
Verify Windows packaging still picks compiled files.
Acceptance Criteria

npm run dev launches the app via compiled dist/main.js.
All existing features work (open/save, panels, filters, paint, rotate, crop, analysis).
No console TS errors; baseline noImplicitAny tolerated initially.
IPC channels and payloads typed in a shared module and used on both sides.
Packaging succeeds and launches on Windows.
Risks & Mitigations

Path/asset resolution from dist: keep relative loadFile paths stable; adjust __dirname usage or copy assets.
Third-party types missing: add minimal ambient typings as needed.
Large diff: migrate per-folder, merge behind feature branch typescript, frequent small PRs.
Milestones

M1: Tooling + main.ts compiles/runs.
M2: Core + Utils migrated.
M3: IPC typed + 2 key renderers migrated (resize, filter).
M4: Remaining renderers migrated.
M5: Enable stricter TS options (noImplicitAny, strictNullChecks).
Try It (local)

Install
npm i -D typescript @types/node @types/electron
Scripts (example)
build:ts: tsc -p tsconfig.json
watch:ts: tsc -w -p tsconfig.json
dev: run npm run watch:ts and electron . (main points to dist/main.js)
Not...

• Fixes Migration to typescript #139

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