build: gate builds on tsc, fix lib floor, correct minAppVersion

The build only ran esbuild, which strips types without checking them — that
is how the week-number ReferenceError shipped. Add a typecheck script and run
it before bundling. It is invoked as 'node node_modules/typescript/bin/tsc'
rather than a bare 'tsc' because this repo's node_modules/.bin entries are
Linux-style symlinks with no Windows .cmd shims, matching how the existing
scripts already call 'node esbuild.config.mjs' directly.

- tsconfig lib gains ES2017 so Object.entries resolves (was TS2550 plus
  cascading TS7031 implicit-any errors); strictness untouched.
- manifest minAppVersion 0.16.3 -> 1.4.4: the plugin calls setTooltip(), added
  in API 1.4.4, so every declared-supported version below that threw
  TypeError on render.
- settings-tab: type plugin as WaypointPlugin via a type-only import (no
  runtime cycle) to drop the (this.plugin as any).saveSettings() cast, and
  make the slider helper generic instead of obj: any. No UI change.
- Add the MIT LICENSE file that package.json and the About tab already claim.

package.json

@@ -5,7 +5,8 @@
 	"main": "main.js",
 	"scripts": {
 		"dev": "node esbuild.config.mjs",
-		"build": "node esbuild.config.mjs production"
+		"typecheck": "node node_modules/typescript/bin/tsc --noEmit",
+		"build": "npm run typecheck && node esbuild.config.mjs production"
 	},
 	"keywords": [],
 	"author": "Olivier",