feat(dev): add TanStack Devtools source inspector in dev builds

[adamleithp]

Problem

The dev-only "Go to Source" helper went missing locally — the one that let you hold a modifier to inspect an element and see exactly which file/line it renders from (via a data-tsd-source attribute on every element). Raised in a Slack thread; folks missed it and confirmed it's fine to add back.

Changes

Adds @tanstack/devtools-vite to the Electron renderer, gated to dev mode, with injectSource enabled. During dev it runs an AST transform that stamps every JSX element with data-tsd-source="<file>:<line>:<col>". Read it in the Elements panel (or hold the inspector hotkey) to jump straight to the source. Excluded entirely from production builds.

How did you test this?

• Ran a standalone Vite dev build with the plugin against a sample component and confirmed the output carries data-tsd-source="…/Comp.tsx:2:10" on the emitted elements.
• electron-vite build evaluates the full config and completes the main bundle with the change in place. (The preload step fails in this sandbox on an unbuilt workspace package; I reproduced the identical failure on a clean tree without this change, so it's pre-existing and unrelated.)

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog from a Slack thread

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 5aa209a.}

[stamphog]

Gates denied this PR because it adds a new dependency (TanStack Devtools) to package.json and pnpm-lock.yaml, which triggers the deps_toolchain deny-list rule. Dependency changes require human review.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(dev): add TanStack Devtools source ..." | Re-trigger Greptile}