[rush reporter][R1] Wire @rushstack/rush-reporter into the Rush toolchain

[TheLarkInn]

Parent: #5858

Goal

Make the standalone @rushstack/rush-reporter package consumable by the live Rush frontend and engine without changing default output.

Scope

• Add @rushstack/rush-reporter as a workspace dependency of @microsoft/rush-lib and @microsoft/rush.
• Update Rush configuration and the PNPM lockfile using the normal Rush workflow.
• Generate and validate the frozen bootstrap-envelope encoder and protocol-major constant used by the zero-dependency install-run-rush bundle.
• Add package-boundary tests proving the reporter package never depends on rush-lib and the generated bootstrap protocol stays in sync.

Acceptance criteria

• rush-lib and apps/rush can import the reporter public API.
• install-run-rush still has no runtime dependency on the reporter package.
• A stale generated encoder/protocol constant fails a targeted test or build check.
• With no reporter opt-in, Rush output remains unchanged.

DAG

Root workstream. Unblocks R2, R3, and R6.

Part of #5858.

[TheLarkInn]

R1 is complete on main. #5985 merged the reporter package wiring, and #5986 merged the generated bootstrap protocol with syntax-tree self-containment checks, undefined-payload normalization, and artifact-owner validation. The current main branch satisfies this issue's acceptance criteria.