Build a scalable, filterable audit log system with a structured event schema

[bridgetthnkechi87-cloud]

Closes #297

Summary

Completed the remaining audit-log gaps on top of the existing structured ActivityEvent system.

Changes

• Added an Entity Type filter to the Activity page
• Removed a duplicate empty refresh button from the Activity page
• Reused the existing ActivityEvent schema from packages/integration-client
• Added tests for entity type filtering and invalid entity type query parsing
• Updated webhook activity mapping to sanitize metadata before storing it
• Added tests proving sensitive webhook fields are stripped
• Added audit log schema documentation with filter, pagination, and datastore migration notes

Notes

The repo already had a structured ActivityEvent schema, cursor pagination, query parsing, and activity storage/query helpers. This PR does not add a parallel schema. It completes the remaining gaps by exposing the existing entity type filter in the UI, tightening webhook metadata sanitization, and documenting the audit log model for future datastore integration.

Testing

• Activity-related tests pass: 149/149
• Full dashboard test suite was run: 624/626 pass, 1 skipped
• The remaining failure is a pre-existing unrelated guild-api.test.ts module-resolution issue, reproduced with this PR's changes stashed out
• tsc --noEmit is blocked by a pre-existing repo-wide --ignoreDeprecations TypeScript config issue