fix(firestore-bigquery-change-tracker): resolve project ID from GOOGLE_CLOUD_PROJECT for Gen2 functions

[davestimpert]

Summary

Fixes project ID resolving to undefined in Gen2 / Cloud Run environments, producing broken SQL like Table undefined:dataset.table.

Root cause — two compounding issues in Gen2:

1. firebase-functions/params's projectID.value() returns "" when FIREBASE_CONFIG lacks projectId. Since "" is falsy, config.bqProjectId || process.env.PROJECT_ID falls through even when a project ID was explicitly passed.
2. PROJECT_ID is not set in Gen2 / Cloud Run — the standard env var there is GOOGLE_CLOUD_PROJECT, which was never checked.

Fix: add GOOGLE_CLOUD_PROJECT to the fallback chain, matching the pattern already used in this repo (e.g. delete-user-data):

preferred || process.env.GOOGLE_CLOUD_PROJECT || process.env.PROJECT_ID

Fixes #2778

Changes

• src/bigquery/gcpProject.ts — new utility resolveGcpProjectIdForBigQuery(preferred?)
• src/bigquery/index.ts — use utility when setting bq.projectId
• src/bigquery/snapshot.ts — use utility in buildLatestSnapshotViewQuery
• src/__tests__/bigquery/gcpProject.test.ts — unit tests covering the fallback priority order

Test plan

• resolveGcpProjectIdForBigQuery unit tests pass (npm test -- gcpProject)
• Existing snapshot unit tests pass (npm test -- snapshot)
• Manual verification in a Gen2 Cloud Function environment

🤖 Generated with Claude Code

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[gemini-code-assist]

Code Review

This pull request introduces a utility function resolveGcpProjectIdForBigQuery to standardize Google Cloud Project ID resolution, prioritizing explicit configuration over environment variables. The changes update the FirestoreBigQueryEventHistoryTracker and snapshot query builder to use this utility. Feedback recommends adding error handling for unresolved project IDs to prevent invalid SQL generation and removing redundant logic in the resolution function.

[cabljac]

Hi @davestimpert do you mind signing the Google CLA agreement? you can click on the CI run it should link you to the form