Document GPT diagnostics attribution and correlation evidence

[prk-Jr]

Summary

• Complete the public GPT Runtime Diagnostics guide against the behavior merged in Attribute GPT renders to Trusted Server on observed evidence #997, so an operator can interpret request-path, delivery, replacement, and attribution evidence rather than only open the console.
• Document the one server-side effect of enabling the integration that the guide never mentioned: the per-auction hb_auction_id correlation token published into window.tsjs.bids, and the targeting boundary that keeps it out of the GAM ad request.
• Remove a stale claim carried over from the pre-Attribute GPT renders to Trusted Server on observed evidence #997 implementation ("No creative-provenance or auction attribution claims") and make the diagnostics guide reachable from the GPT integration page.

Changes

File	Change
docs/guide/integrations/gpt-diagnostics.md	New "Auction correlation token" section (token format, per-auction minting, not EC-derived, not a GAM targeting key, absent without winning bids); badge content and delivery-label table; creative-bridge failure table with the bridge condition that triggers each category; Ad Manager identifier normalization (positive whole numbers, eight-ID list cap); adInit refresh scoped context alongside Prebid's; three new troubleshooting entries for unattributed/competing refreshes, candidate_unconfirmed delivery, and missing correlation evidence (all eight attribution reasons); exact ?ts_console=1 activation and ?ts_console=0 deactivation examples
docs/guide/integrations/gpt.md	Link the diagnostics guide from "Ads Not Rendering" troubleshooting and from "Next Steps"
docs/guide/integrations-overview.md	Replace the stale "no attribution claims" bullet with the delivery-evidence, request-path, and Ad Manager identifier capabilities, keeping the evidence boundary explicit

Closes

Closes #1014

Test plan

• Docs format: cd docs && npm run format
• Docs lint: cd docs && npm run lint
• Docs build: cd docs && npm run build (VitePress build succeeds; #auction-correlation-token anchor and sidebar/integration links resolve in the built output)
• cargo fmt --all -- --check
• JS format: cd crates/trusted-server-js/lib && npm run format
• cargo test-fastly && cargo test-axum — not run: no Rust source changed
• cargo clippy-fastly && cargo clippy-axum — not run: no Rust source changed
• JS tests: cd crates/trusted-server-js/lib && npx vitest run — not run: no JS source changed
• Other: every documented value traced back to source — request paths, opportunities, delivery states, response classes, creative failures, and attribution reasons against crates/trusted-server-js/lib/src/core/types.ts and .../gpt_diagnostics/store.ts; token minting and gating against crates/trusted-server-core/src/publisher.rs; targeting keys against crates/trusted-server-js/lib/src/integrations/gpt/index.ts; badge labels against .../gpt_diagnostics/badges.ts; identifier caps against .../gpt_diagnostics/observer.ts

Checklist

• Changes follow CLAUDE.md conventions
• No unwrap() in production code — use expect("should ...") (documentation only; no code changed)
• Uses tracing macros (not println!) (documentation only; no code changed)
• New code has tests (documentation only; no code changed)
• No secrets or credentials committed — examples use publisher.example.com and a fictional token value