Add one-command website screenshot regeneration

[jongio]

As a contributor updating Dispatch UI states, themes, or website docs, I want a single documented command to regenerate and verify all website screenshots so visual changes are easy to review and do not depend on knowing the Go and Node internals.

flowchart TD
    A[Change TUI or theme] --> B[Run screenshot command]
    B --> C[Capture HTML via cmd/screenshots]
    C --> D[Render PNGs with Playwright]
    D --> E[Review web/public/screenshots diff]

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Problem

The screenshot system is powerful but hard to discover: cmd/screenshots/main.go captures TUI states behind the screenshots build tag, cmd/screenshots/render.mjs requires Playwright, scripts/screenshots.ps1 wires the steps together only for PowerShell, and web/package.json has no screenshot script. Contributors on macOS/Linux or those working from the website package may not know how to regenerate web/public/screenshots consistently.

Proposed solution

Add a cross-platform screenshot entry point, such as go run -tags screenshots ./cmd/screenshots --out web/public/screenshots plus node cmd/screenshots/render.mjs, exposed through web/package.json (npm run screenshots) and a shell wrapper alongside scripts/screenshots.ps1. Document prerequisites and commands in README and the website development docs, add a lightweight CI/check mode that verifies the generator runs against internal/data/testdata/fake_sessions.db, and add tests or script checks around argument parsing/output paths in cmd/screenshots/main.go.

User impact

Contributors can update screenshots confidently in one command, reviewers get reproducible visual diffs, and the website remains aligned with the real TUI states and themes.

Acceptance criteria

• A documented npm run screenshots or equivalent one-command workflow regenerates screenshots into web/public/screenshots from the repo root.
• The workflow works on Windows PowerShell and macOS/Linux shells without requiring contributors to inspect cmd/screenshots internals.
• Playwright and other Node prerequisites are declared in web/package.json or documented with an install command.
• README or contributor docs explain when to run the screenshot workflow and how to review generated diffs.
• A CI-friendly check or test exercises the screenshot capture path against internal/data/testdata/fake_sessions.db without committing transient HTML files.

Complexity

M