fix(logging): add tRPC context to propagate URL params into logs

[danadajian]

Summary

• Introduces a Context type (parsed from the Referer header once per request) that makes SPA URL params available server-side — commitHash, owner, repo, bucket, etc.
• The onError handler now uses ctx.urlParams instead of re-parsing the Referer header itself, consolidating that logic in one place
• acceptVisualChanges now receives ctx so its INFO log automatically includes all URL params without manually enumerating owner, repo, hash, etc.
• tRPC procedure inputs are unchanged — context is used only as a cross-cutting concern, preserving full type-safe contracts between client and server

Changes

• app/backend/src/context.ts (new) — Context type and createContext function; parses Referer header into urlParams
• app/server.ts — passes createContext to createBunHttpHandler; onError uses ctx?.urlParams instead of inline Referer parsing
• app/backend/src/router.ts — initTRPC.context<Context>().create(); passes ctx to acceptVisualChanges mutation
• app/backend/src/acceptVisualChanges.ts — accepts ctx: Context as second param; spreads ctx.urlParams into the VISUAL_CHANGES_ACCEPTED info log
• app/backend/test/acceptVisualChanges.test.ts — updated call sites to pass { urlParams: {} } as ctx

Test plan

• Trigger acceptVisualChanges and verify the server INFO log includes owner, repo, bucket, commitHash from the browser URL
• Trigger a tRPC error and verify the ERROR log still includes URL params via ctx.urlParams
• bunx nx test backend passes

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🎉 This PR is included in version 1.41.3 🎉

The release is available on GitHub release

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