docs(readme): streamline LFM2.5 quickstart for Expo

[msluszniak]

Description

Tightens the LFM2.5 quickstart in the root README and all five translated readmes:

• Flags the quickstart as Expo-targeted and links bare React Native users to the Getting Started guide instead of duplicating the bare install steps inline.
• Drops the react-native-executorch-bare-resource-fetcher / @dr.pogodin/react-native-fs / @kesha-antonov/react-native-background-downloader lines from the install snippet now that the bare path lives in the docs.
• Switches the sample to the model-registry accessor (models.llm.lfm2_5_1_2b_instruct()), matching the apps and the new MODEL_REGISTRY flow added in feat(constants)!: switch URLs to v0.9.0 layout + add MODEL_REGISTRY #1148.
• Normalizes yarn <ios|android> placeholders — no spaces inside the angle brackets.

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

Docs-only change. Render the affected readmes on GitHub and confirm:

• Quickstart heading is followed by the Expo / bare-RN doc-link sentence.
• Install block lists only the Expo fetcher trio.
• Code sample imports models and calls models.llm.lfm2_5_1_2b_instruct().
• No < ios | android > (with spaces) remains.

Screenshots

N/A

Related issues

N/A

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes

The translated readmes carry through the same edits with the disclaimer + doc link translated into each language; the docs URL is shared across all of them.