Adopt @screenly-labs/signage-kit for degraded mode

[vpetersson]

Part of the fleet-wide adoption of @screenly-labs/signage-kit: this app now consumes the shared degraded-mode pipeline (support floor, CSS down-level recipe, JS bundler, inline gate, replaceChildren polyfill, and the html.legacy kill-switch) instead of its own inlined copies.

Purely mechanical — behaviour is unchanged. Build output verified equivalent:

• @layer in built CSS: 0
• html.legacy kill-switch present: yes (3)
• :lang( in built CSS: 0
• gate injected into dist/index.html: yes (classList x2)
• es-check es2017 dist/static/js/main.js: passes
• JS format: IIFE (index.html loads a classic <script defer>)

typecheck, lint, and test all pass.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR migrates the app’s “degraded mode” implementation (support floor, inline gate, CSS down-leveling recipe, JS bundling, and polyfills) from app-local copies to the shared @screenly-labs/signage-kit pipeline, aligning this repo with the fleet-wide rollout while keeping the shipped output equivalent.

Changes:

• Add @screenly-labs/signage-kit and switch the build pipeline to injectGate, processCss, and bundleJs.
• Replace the inline degraded-mode gate in index.html with build-time injection.
• Use the kit’s shared CSS preset + polyfills, removing the app-local polyfills shim and legacy CSS kill-switch block.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
package.json	Adds @screenly-labs/signage-kit and removes the in-repo browserslist config block.
bun.lock	Locks @screenly-labs/signage-kit GitHub dependency resolution.
build.js	Replaces inlined CSS/JS build logic and gate injection with signage-kit helpers.
index.html	Removes the inline degraded-mode gate script in favor of build-time injection.
assets/static/styles/tailwind.css	Imports the kit preset and removes app-local degraded-mode kill-switch CSS.
assets/static/js/main.ts	Switches to the kit-provided polyfills side-effect import.
assets/static/js/polyfills.ts	Deletes the app-local replaceChildren shim (now provided by the kit).

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