feat(web): dev server runs devknobs from the local checkout

[mertbuilds]

Summary

• the dev server now runs devknobs from a local checkout's source (src/index.ts), so the site is the test bed for the panel and edits there reload the page
• checkout is DEVKNOBS_PATH (absolute or relative to the repo root), else ../devknobs beside the repo, which also fits knobs.dev.<branch> worktrees
• dev start logs which devknobs is in use; build, preview, ci and prod keep the pinned npm package

Test plan

• lint, format:check, typecheck, build
• build output has no reference to the local checkout
• dev: page 200, devknobs served from the local path, bezel images 200
• edit in the devknobs checkout reloads the site

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Summary by cubic

The dev server runs devknobs from a local checkout so the site tests the panel in progress and edits there reload. Build, preview, CI, and prod keep the pinned npm package, now bumped to 0.1.0.

• The checkout comes from DEVKNOBS_PATH (absolute, or relative to the repo root), else ../devknobs beside the repo; dev start logs which devknobs is in use, and bezel images map from the checkout's assets/bezels.
• The early script is injected ahead of React's head content so a reload with a device set keeps the frame; in dev the plugin rebuilds it from the checkout when its sources change.
• The page presents devknobs 0.1.0: the iPhone Duo (fold and unfold), mat colors, new default keys, and panel settings, with the try buttons split into device and knob groups.
• Font sizes and page line heights are now in rem so the text size knob scales the page text.

^{Written for commit 839e054. Summary will update on new commits.}