fix(dev): Linux tauri:dev startup failures (WebKitGTK load + i18n mount race)

[Raymond8196]

Summary

Fixes #508 — on Linux, pnpm tauri:dev fails to reach the main UI due to two
related dev-only startup failures.

Two coordinated, dev-only commits; production builds are untouched.

Commit 1 — fix(dev): keep App bundled into main.js so WebKitGTK can load it

Since e06f4b471, App is loaded via a runtime dynamic import("@src/App"),
which webpack emits as a separate chunk. Under eval-cheap-module-source-map
that chunk inlines every module's source and balloons to ~77MB; WebKitGTK
fails the runtime dynamic import → "Initialization Failed".

• src/index.tsx: in dev, mark the App import with
  /* webpackMode: "eager" */. App is bundled into main.js instead of
  being a separate runtime chunk, while import() keeps its Promise-returning
  semantics (so App module-tree eval still runs after the runtime-identity
  config). Production keeps the normal dynamic import.
• webpack.config.js: dev devtool switches from
  eval-cheap-module-source-map to cheap-source-map (separate lazily-loaded
  .map file), keeping the executable main.js at ~41MB with line-level
  debuggability. Cost: incremental dev rebuilds are marginally slower.

Commit 2 — fix(dev): await i18n before React mount to avoid store-undefined crash

On a slow cold start the parallel init Promise.all loses the 10s
Promise.race; the rejection was swallowed and React mounted before
i18n.init() completed, crashing the first useTranslation() call on
i18next's not-yet-initialized this.store.

i18n is not degradable (App calls useTranslation() unconditionally at
render), so pull i18nReady out of the bounded race and await it
unconditionally after the degradable ops settle. It still starts at module
load and runs parallel to the other ops, so the await only blocks when
locale bundles are genuinely still loading. On rejection, surface the
emergency error UI instead of mounting a guaranteed-to-crash React tree.

Production safety

• webpackMode: "eager" is gated behind isDev (compile-time). Production
  keeps the normal dynamic import.
• The devtool change is dev-only: useDevSourceMaps = !isProduction && ...,
  so production devtool stays false.
• The i18n await change is runtime code but correct regardless of build:
  i18n must be initialized before React renders useTranslation() consumers.

Test plan

• pnpm tauri:dev on Linux reaches the main UI (no "Initialization Failed")
• First cold launch no longer crashes with hasLanguageSomeTranslations;
  no manual reload needed
• eslint src/index.tsx — clean
• tsc --noEmit — no new errors (3 pre-existing errors in
  src/modules/ProjectManager/ are unrelated to this change)
• Reviewer: confirm pnpm tauri:dev on macOS is unaffected
• Reviewer: confirm production build (pnpm tauri:build) is unaffected

Verified on Ubuntu 22.04 / WebKitGTK. Regression range: since e06f4b471.