fix(eve): preserve receive-only channels

[glucas1103]

Description

Closes #1270.

compileChannelDefinition() currently lowers channels by mapping their routes. A channel with routes: [] and an authored receive hook therefore emits no manifest entry, disappears from the module map, and cannot be resolved by schedules or cross-channel handoffs unless the application invents a placeholder HTTP route.

This change adds a first-class receive-only-channel manifest entry. Receive-only channels remain discoverable and resolvable through the normal authored-module path, appear in eve info and the Vercel agent summary without route metadata, and are excluded from Nitro route registration. The docs, schema versions, runtime types, compiler/runtime coverage, and patch changeset are updated together.

How did you test your changes?

• pnpm test:unit — 5,462 tests passed, 1 skipped.
• pnpm test:integration — 550/550 tests passed.
• pnpm typecheck
• pnpm docs:check
• pnpm lint
• pnpm guard:invariants

PR Checklist

• I linked an issue with prior discussion confirming this change is wanted
• I ran the relevant checks from CONTRIBUTING.md
• I added tests and documentation where relevant
• I added a changeset if this touches the published eve package
• DCO sign-off passes for every commit (git commit --signoff)

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Additional Suggestions:

1. Next.js chat/workflow info validator throws on receive-only channels because it still requires channel.method/channel.urlPath to be strings after the agent-info schema made them nullable.

2. Receive-only channels cannot be resolved via the route-fingerprint fallback in resolveTargetByReference, so schedules/cross-channel handoffs targeting them throw "not registered" whenever reference identity does not hold.