fix(typecheck): enable @ts-check on packages/superdoc/src/index.js

[caio-pizzol]

First debt drain on the JSDoc ratchet snapshot. packages/superdoc/src/index.js was the only file under packages/superdoc/ on the 103-entry public-reachable debt list; this PR moves it from "tracked debt" to "fully gated by // @ts-check". Snapshot count: 103 → 102.

Tight diff: 2 files, +5/-3 lines.

Two type errors surfaced and got fixed

1. ./core/theme/create-theme.ts import had an explicit .ts extension - TS rejects this without allowImportingTsExtensions. Changed to .js. The rest of the file already uses .js (the canonical convention), and packages/superdoc/src/public/index.ts:55-56 imports the same module via .js.

2. '@superdoc/common/data/blank.docx?url' Vite asset import has no static type. Suppressed with // @ts-expect-error - same pattern src/public/index.ts already uses.

Why per-file @ts-expect-error instead of a global *?url ambient shim

I tried the cleaner ambient approach first (packages/superdoc/src/shims-url.d.ts declaring *?url). It let the import resolve cleanly, but vite-plugin-dts then preserved the @superdoc/common/data/blank.docx?url import statement in the emitted public/index.d.ts, which tripped audit-declarations.cjs's "private workspace specifier" rule. Per-file suppression keeps the import "unknown" from TS's perspective, which keeps it from leaking into the .d.ts. The longer-term fix (rewriting ?url specifiers in ensure-types.cjs so the ambient shim is safe) is a separate piece of work.

Verified

• pnpm check:types → PASS (tsc -b clean across all referenced projects)
• pnpm check:public:superdoc → PASS, 9 stages, 156s. The jsdoc-ratchet stage now reports OK 6 CHECKED_FILES clean; ratchet snapshot in sync with index.js properly accounted for via // @ts-check rather than the debt snapshot.
• audit-declarations.cjs (postbuild) → clean. No @superdoc/* specifier leak.

What this is NOT

• Not a TS migration. The file stays .js; just type-checked.
• No intended public-surface change. Same export blocks, same JSDoc typedef re-exports.
• Not "fix everything in src/superdoc". Other files (stores/superdoc-store.js, core/surface-manager.js, core/create-app.js) are not on the public-reachable surface, so adding // @ts-check there wouldn't drain the snapshot. Pick those up only if the goal becomes "harden internals", not "drain known debt".

Snapshot diff

packages/superdoc/scripts/jsdoc-debt-snapshot.json: one line removed (packages/superdoc/src/index.js). 102 entries remain - all under packages/super-editor/src/editors/v1/**.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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