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.

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Olivier
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.