Refactor the TypeScript data flow for full type safety and auto-generation of Rust types (#3865)

* Migrate Specta to Tsify to auto-generate messages.ts, working except colors and widgets

* Adopt the generated FillColor/Color/GradientStops

* Fix widget typing

* Separate WidgetGroup enum variants into wrapper structs

* Small rename

* Simplify widgets further

* Clean up message type references

* Switch type imports to the auto-generated file

* Remove lowercase serde rename

* Fix FillChoice deserialization

* Fix small regression from #3837

* Improve type safety

* Make WidgetSpan type-safe

* More cleanup and type safety

* More type safety

* More type safety

* Get the rest to type-check without errors; improve widget builder macro to have optional icons; improve Svelte 5 configs

* Cargo fmt

* Fix imports

* Update outdated readme info

* Fix lint command rename references

* Fix typos

* One more typos fix

* Remove unnecessary dep: prefix from the edited Cargo.toml files

* Remove excess parts from Cargo.toml

* Fix compiling on desktop

* Revert "Remove excess parts from Cargo.toml"

This reverts commit 6b711117b3a5d5d8a3ee20f36a43bc74930b7c82.

* Update dev docs with simpler, more accurate instructions

frontend/package.json

@@ -15,8 +15,8 @@
 		"build-native": "npm run setup && npm run native:build-production",
 		"build-native-dev": "npm run setup && npm run native:build-dev",
 		"---------- UTILITIES ----------": "",
-		"lint": "eslint . && tsc --noEmit",
-		"lint-fix": "eslint . --fix && tsc --noEmit",
+		"check": "svelte-check --fail-on-warnings && eslint",
+		"fix": "eslint --fix",
 		"---------- INTERNAL ----------": "",
 		"setup": "node package-installer.js && node branding-installer.js",
 		"native:build-dev": "wasm-pack build ./wasm --dev --target=web --no-default-features --features native && vite build --mode native",
@@ -45,6 +45,7 @@
 		"eslint-plugin-prettier": "^5.5.5",
 		"eslint-plugin-svelte": "^3.14.0",
 		"globals": "^17.0.0",
+		"svelte-check": "^4.4.4",
 		"license-checker-rseidelsohn": "^4.4.2",
 		"postcss": "^8.5.6",
 		"prettier": "^3.8.0",