chore(module): trim stale PR-I genesis-tag rationale in module/doc.go

[trilamsr]

Context

Post-wave-audit finding #8 (see docs/v1-rc1-post-wave-audit.md).

module/doc.go documents the genesis-tag rationale for PR-I.1a / PR-I.1b / PR-I.2:

// moved out of the root module per RFC-0013. Contents land in PR-I.1b (nccl_fr move)
// and PR-I.2 (rankjoinprocessor + patterndetectorprocessor).
//
// This file exists so that `module/v0.0.1` (the genesis tag cut after PR-I.1a
// merges) resolves through the Go module proxy ...

All three PRs landed long ago. The "Contents land in…" framing is now a historical artifact, and the genesis-tag rationale is no longer load-bearing (the module is alive and well).

Fix

Trim to:

// Package module hosts in-repo Go submodule for receivers/processors/exporters
// moved out of the root module per RFC-0013.
package module

8-line deletion.

Acceptance

• module/doc.go carries package doc only.
• No PR-I sequence references.
• go list -m github.com/tracecoreai/tracecore/module still succeeds (the file still has a package module declaration, which is the proxy requirement).