fix(logging): include URL params and simplify TRPCError cause

[danadajian]

Summary

• Parses the Referer header in the onError handler to extract all SPA URL parameters (commitHash, owner, repo, bucket, etc.) and spreads them into every error log entry
• This ensures URL params are available in error logs even for procedures (e.g. fetchCurrentPage) that don't receive owner/repo as tRPC inputs
• Simplifies all TRPCError cause fields from objects ({ event: 'FOO', owner, repo, ... }) to plain event name strings ('FOO') — the extra context is now sourced from the URL params

Changes

• app/server.ts — onError now extracts urlParams from req.headers.get('referer') and logs them alongside cause; input removed (superseded by URL params)
• app/backend/src/fetchCurrentPage.ts — cause simplified to string in both throws
• app/backend/src/getGroupedKeys.ts — cause simplified to string in both throws
• app/backend/src/acceptVisualChanges.ts — cause simplified to string in both throws
• app/backend/src/getOctokit.ts — cause simplified to string in all three throws
• app/backend/src/updateCommitStatus.ts — cause simplified to string

Test plan

• Trigger a fetchCurrentPage error (e.g. invalid hash) and verify the server log includes owner, repo, bucket, commitHash from the browser URL alongside the cause event name
• Verify no TypeScript errors (bun tsc)

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🎉 This PR is included in version 1.41.2 🎉

The release is available on GitHub release

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