feat(react)!: extract React Router relaxations into an optional group

[stevensacks]

What

react shipped a block scoped to **/routes/**/*.tsx that turned no-empty-pattern off. That glob is not unique to React Router, since TanStack Router uses a routes/ directory too, so a project on any other file-based router had the rule silently disabled across its whole route tree with nothing in the composed config explaining why.

The relaxation moves into a new opt-in reactRouter block:

...lint.react,
...lint.reactRouter,   // React Router framework mode only

Why this is a major

Unlike storybook and playwright, which only ever add rules, this block is subtractive. Making a subtractive block opt-in is inherently breaking: React Router consumers must add the spread to keep current behavior. Migration is that one line, and a project that never writes ({}: Route.ComponentProps) sees no new errors either way.

Verification

Measured against GAIA's real tree rather than assumed:

• ({}: Route.ComponentProps) errors outside routes/ and is suppressed inside it, so the exemption is load-bearing rather than vestigial.
• no-empty-pattern forced on across app/routes reports zero violations today, so GAIA's own upgrade is a no-op.
• New suite asks ESLint what the composed config resolves to on both sides of the opt-in, so folding the block back into react, or widening its glob, fails a test instead of quietly relaxing a rule.

Dead config removed

Two entries in the blocks being touched, both verified to change no effective rule anywhere:

• react/display-name was set to off in the route block, but airbnb/config/react already sets it off for every file.
• The typescript/only-throw-error block disabled that rule for hooks/, routes/, and sessions.server/, but typescript/config already disables it globally for **/*.ts?(x).

Notes

The /.react-router/** glob stays in the ignores defaults. It names a directory that only exists in a React Router project, so it costs other projects nothing, while moving it would break React Router consumers who miss the new spread.

A TanStack Router group (wrapping @tanstack/eslint-plugin-router) is deliberately not in this PR. It is purely additive, so it can land as a minor without a migration.

An audit of the whole composed config turned up ~28 further dead rule entries beyond the two removed here. Out of scope for this PR; will be raised separately.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MN1TCLUXUHLv9PBPBaL3fg