fix(tanstack-start): pin solid-js to 1.x for devtools peer

[stormslowly]

Why

The rspack ecosystem CI run fails at build:rsbuild on rsbuild/tanstack-start with 64 module linking errors:

× ESModulesLinkingError: export 'onMount' (imported as 'onMount') was not found in 'solid-js'
× Package subpath './web' is not defined by "exports" in .../solid-js/package.json

@tanstack/devtools declares solid-js: >=1.9.7 as a peer dependency. Since #495 introduced solid-js@2.0.0-rc.0 into the workspace, a full re-resolution (which ecosystem CI triggers by injecting @rspack/* overrides) dedupes that peer onto 2.0.0-rc.0 instead of the package's own solid-js: ^1.9.9 dependency. Solid 2 removed onMount / batch / on / getListener and the ./web subpath export, so the devtools bundle no longer links.

Before / after, same install (pnpm install --prefer-frozen-lockfile with @rspack/* overrides injected):

	@tanstack/devtools resolves to	rsbuild/tanstack-start build
before	solid-js@2.0.0-rc.0	fails, 64 errors
after	solid-js@1.9.13	passes

What

Declare solid-js: ^1.9.9 in rsbuild/tanstack-start, so this example provides the peer itself and its subtree stays on Solid 1.x. The Solid 2 RC in rsbuild/solid is untouched.

Rejected alternatives: dedupePeers: false (does not change the resolution), and a workspace-wide solid-js override (would downgrade the Solid example and undo #495).

Verified locally by running the full ecosystem CI sequence — build:rspack:eco-ci, test:rspack:eco-ci, build:rsbuild, build:rsdoctor, build:rspress, build:rslib — plus pnpm lint.