build: make npm run start work from a clean checkout

[ubugeeei]

Finding

README directs users to npm run start, but start maps to dev:bin, which can require generated binaries that are ignored by git. A clean checkout should have an obvious first-run command that works or fails with precise setup guidance.

Evidence

• package.json start -> npm run dev:bin.
• bin is ignored in .gitignore.
• Electron binary lookup falls back to bin//backend and bin//render in packaged/bin mode.

Acceptance criteria

• Decide whether start should run source/dev mode or build binaries first.
• Update scripts and docs so clean-checkout startup is reliable.
• Preserve explicit bin-mode commands for production-like local runs.

[ubugeeei]

対応済みです。修正は PR #1 / commit 9cf4498 に反映済みです。