[jhuleatt]

Summary

Previously, vite.config.ts bundled all of src/* into a single monolithic dist/index.js that imported every Firebase product (firebase/firestore, firebase/auth, firebase/database, firebase/storage, firebase/functions, firebase/remote-config, firebase/performance) at the top of one file. Because all product imports lived inside a single pre-bundled chunk, consumer bundlers could not tree-shake unused Firebase SDKs or split them behind React.lazy.

This PR:

1. Emits one ES module per source file (preserveModules: true, preserveModulesRoot: 'src', entryFileNames: '[name].js') alongside dist/index.umd.cjs.
2. Externalizes rxjs, rxjs/operators, and rxfire/* (declared in dependencies) so consumer bundlers resolve and tree-shake them directly instead of inlining a duplicate copy.
3. Updates "rxjs" in dependencies from "^6.6.3 || ^7.0.1" to "^7.1.0" so external resolution always provides RxJS ≥ 7.1 (required by share({ resetOnRefCountZero: () => timer(...) })).
4. Adds "sideEffects": false to package.json.
5. Sets "target": "es2024" in tsconfig.json (Baseline-certified) so TypeScript does not inject virtual _tslib.js helper chunks under preserveModules: true.

Bundle Size Impact

Measured with Vite 8.3.5 production builds against firebase@13.1.0 (gzip -9 of the emitted application bundle):

Consumer App	Raw Firebase Baseline (No ReactFire)	reactfire@4.2.6 (main)	With This PR (preserveModules: true)	Savings vs. 4.2.6
Auth-only (useUser)	96.0 KB (95,988 B)	269.1 KB (269,074 B) — bundles Firestore, RTDB, Storage, Perf, Functions, RC	103.8 KB (103,791 B) — only firebase/auth + rxjs + rxfire/auth	-165.3 KB gzip (-61.4%)
Firestore-only (useFirestoreCollection)	206.8 KB (206,792 B)	279.0 KB (279,049 B) — bundles Auth, RTDB, Storage, Perf, Functions, RC	214.5 KB (214,541 B) — only firebase/firestore + rxjs + rxfire/firestore	-64.5 KB gzip (-23.1%)

Backwards Compatibility & Release Notes

• Identical Public Exports (74 / 74): Both import * as RF from 'reactfire' (dist/index.js) and require('reactfire') (dist/index.umd.cjs) expose the exact same 74 named exports as v4.2.6.
• Unchanged Entrypoints: package.json "main" (dist/index.umd.cjs), "exports" ("." -> { "import": "./dist/index.js", "require": "./dist/index.umd.cjs" }), and "typings" (dist/index.d.ts) are unchanged.
• Safe "sideEffects": false: All globalThis caches (_reactFirePreloadedObservables, _reactFireFirestoreQueryCache, _reactFireDatabaseCachedQueries) are initialized inside the modules that read them (useObservable.ts, firestore.tsx, database.tsx), so dropping an unused product module (e.g., dist/database.js or dist/performance.js) never drops state needed by used modules.
• Release Note (rxjs ^7.1.0): Because rxjs is a regular dependency (and v4.2.6 already bundled rxjs@7.8.1), runtime behavior and npm install are unchanged. However, TypeScript applications still on rxjs@6 that pass their own custom Observable instances directly into useObservable or preloadObservable will need to upgrade to rxjs@^7.1.0 so TypeScript's Observable types match.

Closes #489
Closes #488
Refs #480