Add first-party Think instrumentation

[RulaKhaled]

Cloudflare Think (@cloudflare/think) — opinionated Workers agent harness.

First-party Orchestrion / Node auto-instrumentation. Zero-config. Target: v11. Approach TBD after investigation.

Related: #22325, TET-2715.

**Refs: **@cloudflare/think · Project Think

[linear-code]

JS-3568

[RulaKhaled]

Merged #24660 (cloudflare-think e2e app) and #24700 (Vite plugin keeps the user's class name).

Think needs no first-party instrumentation. A worker with zero Sentry imports gets the full invoke_agent / generate_content / execute_tool hierarchy with usage, prompts, tool args and finish reasons: the Vite plugin wraps extends Think at build time and vercelAIIntegration reads the ai telemetry. Tool errors, manual spans inside tools and dataloader spans all land in the same trace. The only bug was ours, the class rename mangling the agent span name, fixed in #24700.

One gap, not Think-specific: Think's cloudflare.agents.turn.* context (runtimeContext on v7, experimental_telemetry.metadata on v6) is read by neither subscriber. Tracked in #24720 (v6 metadata, #24721 fixes it) and #24706 (v7 runtimeContext).