[tdody]

Adds periscope's product and design context, written by Impeccable's init and document runs, so every worktree and every agent reads the same thing.

What's in it

• PRODUCT.md: who periscope is for, what it's for, the four positioning claims, and five product principles. Tom, this is the part to push back on. It says the maintainers' daily loop breaks ties over installers, and it calls Clawd and the critters core identity.
• DESIGN.md: the design system as it stands in static/styles.css, under the North Star "The Sonar Screen". It covers the palette with sonar names, the type scale, layout, elevation, components, and do's and don'ts. It records what the CSS does today, including its known drift, rather than an ideal.
• .impeccable/design.json: the machine-readable copy of DESIGN.md that Impeccable's tools read.
• .impeccable/live/config.json: tells Impeccable's live mode to inject its script into static/index.html and static/history.html.
• .gitignore: ignores Impeccable's per-run and per-developer files (critique snapshots, live-mode sessions and annotations, config.local.json). .impeccable/critique/ignore.md stays tracked.

Why commit it

• A worktree made from origin/main doesn't see untracked files, so design work there started without this context.
• A PR that changes the CSS can update DESIGN.md beside it, so drift shows in review.
• The rail tickets from the critique (THI-456 to THI-461) cite these principles. Agreeing on them first is cheaper than arguing inside each PR.

No code changes. Nothing in the files is secret.

Assumptions to challenge

• PRODUCT.md's voice section was read from the README and CHANGELOG, not confirmed separately.
• Impeccable's docs say critique snapshots ignore themselves. Here they didn't, so the root .gitignore handles them.

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