DEV: Type-check with TypeScript 7 - #43406

Bundled plugins and themes now take `@discourse/types` from the pnpm workspace and reference the core project, so `tsc -b` builds core declarations first and checks every plugin against them in the same run. A core type change no longer needs a package release and a version bump before plugins see it, and the language server resolves core imports straight to core source.

- Every plugin and theme depends on `discourse` as `workspace:@discourse/types@*` and lists `frontend/discourse` in `references`.
- The shared plugin config writes each project's build info next to its own `tsconfig.json`, since all of them used to share one path under `declarations`.
- `pnpm install` regenerates the external type stubs through a `prepare` script, so a fresh checkout has them before the first type check.
- The publish workflow keeps publishing `@discourse/types` for plugins outside this repository and no longer opens a bump PR.
- An integrity spec drives the TypeScript language server from a plugin file and checks that "go to definition" on core `.ts`, `.js`, `.gts` and `.gjs` imports lands in core source.

`typescript` now resolves to the TypeScript 7 nightly, so `tsc` is tsgo across the repository and the scripts no longer need the `typescript-7` alias. TypeScript 6 stays only where a tool uses the TypeScript JavaScript API, which TypeScript 7 does not ship.

- ESLint keeps TypeScript 6 through `@discourse/lint-configs`, which depends on it directly. A package extension gives lint-configs its own `@typescript-eslint/parser`. Without it, the parser that `ember-eslint-parser` asks for as a peer resolved `typescript` from the root.
- The `typescript` override now only applies to `@glint/tsserver-plugin`, which still runs inside the TypeScript 6 server in editors. The repository-wide override also rewrote peer ranges, which hid that `eslint-plugin-tsdoc` pins an older `@typescript-eslint/utils` that does not accept TypeScript 6. That plugin now uses the same `@typescript-eslint/utils` as the rest of lint-configs.
- `discourse-i18n` emits its declarations with `tsc` instead of Glint's `ember-tsc`.
- `@discourse/types` has TypeScript 6 as a dev dependency, because `dts-generator.ts` uses the compiler API.
- Glint's `ember-tsc` now gets TypeScript 7 as its peer. The content mapper only uses its template transform, which does not load `typescript`.

`dts-generator.ts` now reads declaration files through the TypeScript 7 API, so `@discourse/types` no longer needs TypeScript 6. The generated stubs are byte-for-byte the same as before.

- The generator only ever needs to wrap and rewrite `.d.ts` files. A few packages also ship `.ts` sources, but the declarations emitted from them never reached the output, so that path is gone along with its diagnostics handling.
- `isDeclaredExternalModule` is gone too, since `generate-external-types.js` never read it.
- TypeScript 7 has no JavaScript parser, so the generator starts a tsgo process through `typescript/unstable/sync` and reads each file's syntax tree from it. That API is marked unstable and may change between TypeScript 7 releases.

`typescript` moves to `7.1.0-dev.20260930.4`, `@glint/ember-tsc` to 1.11.6 and `@glint/tsserver-plugin` to 2.7.9. `ember-content-mapper` 0.3.1 and `@glint/template` 1.9.0 are already the latest releases.

- This is the newest nightly without microsoft/TypeScript#64656. From `7.1.0-dev.20261001.1` on, declaration emit fails with TS5088 on an inferred type that refers to itself, where earlier versions wrote `any` at the cycle. Seven places in core hit it.
- In newer nightlies, the sync API's `createProgram` takes the compiler options as its second argument. `dts-generator.ts` now passes an empty object there, which works with both forms.

The backend job deletes `node_modules` before running RSpec, so the language server spec had no `tsc` to start and failed with `EOFError`. The same check is now a `node:test` file in `@discourse/types`, which runs in the linting workflow next to the type check, where `node_modules` is present.

- It opens a plugin file in the TypeScript 7 language server and checks that "go to definition" on core `.ts`, `.js`, `.gts` and `.gjs` imports lands in core source, and that the file has no diagnostics.
- When the server exits early, the failure includes the server's stderr.
- `pnpm --dir=frontend/discourse-types test` runs it locally.

The VS Code recommendations, the devcontainer and the types guide named the extension `TypeScript.native-preview`, which does not exist. Its ID is `TypeScriptTeam.native-preview`, and the Marketplace now calls it TypeScript 7, so the guide uses that name.

`block-outlet.gts` passes the outlet info debug component a default block, but its copy of that component's signature declared no blocks. With strict mode on, TypeScript 7 reports this as an implicit `any` at both call sites. Glint's `ember-tsc` drops the error, because it lands on generated code with no source position.

lint-configs 3.8.1 lists `@typescript-eslint/parser` as its own dependency, so ESLint's parser now finds the TypeScript 6 that lint-configs installs, with no help from core. The `packageExtensions` entry that added the parser for it is gone.

The JSDoc typedef described the positional args as `Args.Positional.0` and `[Args.Positional.1]`. TypeScript 7 writes those into the declaration file as properties with no name, which TypeScript 5 and 6 cannot parse. Themes and plugins include every declaration file from `@discourse/types`, so this one file failed their whole type check. A labeled tuple gives the same types and keeps the descriptions in the labels.

lint-configs 3.8.2 lints with TypeScript 5.9, which the `@typescript-eslint/utils` version that `eslint-plugin-tsdoc` pins accepts. The override that moved that plugin onto a newer `@typescript-eslint/utils` is gone.

The skill described `pnpm lint:types` as `ember-tsc -b`, and its conversion reference named `ember-tsc` as the check that misses runtime module-resolution errors. Both now name `tsc`. The guidance itself is unchanged.