Add crashlytics sdk setup guides to readmes

[tonybaroneee]

Preview: https://github.com/firebase/firebase-js-sdk/blob/crash-setup-docs/packages/crashlytics/README.md

[changeset-bot]

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Latest commit: 2e74979

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[gemini-code-assist]

Code Review

This pull request introduces comprehensive setup guides and documentation for Firebase Crashlytics for Web Apps, covering frameworks like Angular, Next.js, React, and React Router, along with reusable documentation partials. The review feedback highlights several critical issues in the documentation examples: incorrect shell variable placeholders and unquoted JSON values in the main README, a misleading comment regarding log exclusion levels, a Next.js serialization runtime error caused by passing a non-serializable FirebaseApp instance in a Server Component layout, and a copy-pasted Next.js layout example in the standard React guide.

[PolinaGo]

Reviewing files 1-by-1, starting with the top one

[tonybaroneee]

@jwolfson-goog @PolinaGo

📝 Overview of Changes & Review Feedback Addressed

1. Project Configuration & Setup Flow

• Automated Firebase Console Setup: Promoted the automated setup via the Firebase Console Crashlytics page as Option 1 (recommended).
• Removed Cloud Console UI Steps: Removed manual Cloud Console UI setup steps to streamline instructions while keeping the gcloud CLI steps (Option 2) for command-line and agent-driven workflows.
• Firebase Terms of Service Note: Added a note reminding users onboarding from existing Google Cloud projects to accept the Firebase Terms of Service in the Firebase Console prior to setup.
• Sequential Flow: Restructured the setup into logical steps (Step 1: Project Setup, Step 2: Core SDK Setup, Step 3: Framework Integration) with an explicit note requiring Steps 1 & 2 to be completed first.

2. EAP Access & Prompt Updates

• EAP Notice: Added a private preview notice at the top of the README with a link to the EAP sign-up form.
• Agent Setup Prompt: Made the entire Agent Setup Prompt block copy-able in a single snippet and updated instructions to point to the GitHub README files instead of PDF documents.

3. Framework-Specific Guides & Documentation Layout

• TanStack Router: Moved TanStack Router setup into its own dedicated guide (packages/crashlytics/src/tanstack/README.md) and kept react-router/README.md focused on React Router v6+.
• Folder & File Renaming:
  • Renamed the partials/ directory to docs/ and updated .gitignore rules so files are tracked.
  • Renamed _gotchas_absence_of_log.md to _custom_attribute_collection.md and updated the section heading to Custom Attributes in the Absence of log() Method.
  • Moved Alerting, Sampling, Telemetry Collection, Log Schema, and App Versioning into standalone doc files under docs/ and linked to them under Additional Configuration & References.
• Cleanup: Removed the duplicate Feedback & Support section at the end of the README.