[rush reporter][R3] Emit shadow RushSession lifecycle and diagnostics

[TheLarkInn]

Parent: #5858

Blocked by: #5974

Goal

Connect rush-lib to the reporter event contract in shadow mode, with no visible output change.

Scope

• Expose a typed reporter event sink and scoped producers through RushSession, actions, and plugins without exposing concrete reporters.
• Adapt command/session lifecycle, structured diagnostics, telemetry projection, and command-result/exit-status events into the canonical envelope.
• Keep operation identity phase-aware: an operation is project × phase, not merely a project.
• Bridge legacy hooks and AlreadyReportedError correlation while the legacy renderer remains authoritative.
• Add parity tests for event ordering, telemetry fields, diagnostics, and exit status.

Acceptance criteria

• Shadow emission can be enabled in tests without changing stdout/stderr.
• First-party lifecycle and diagnostic paths emit stable, correlated envelopes.
• Actions/plugins receive scoped producer APIs only.
• Telemetry and derived exit status match legacy behavior for success, warning, failure, cancellation, and internal-error cases.
• Phase-aware operation identifiers are stable across retries/watch iterations.

DAG

Unblocks R4, R5, and R7.

Part of #5858.

[TheLarkInn]

R3 implementation is complete and stacked in order: #5985 -> #5988 -> #5991 -> #5992. I independently reviewed #5988 and #5991 against this issue/RFC phase 3; no parent-slice defect required rewriting those branches. #5992 adds the exhaustive parity/integration matrix and fixes logical-cancellation derivation while preserving legacy output and authoritative process exit behavior. Local reporter/rush-lib/rush/rush-sdk tests, builds, API review, rush check, and change verification pass. Current blocker: #5985 has green CI and squash auto-merge enabled but still requires maintainer approval. Child PRs remain on their parent branches with only CLA checks; they must be retargeted to main one at a time after each parent merges, then pass full CI and approval before enabling squash auto-merge. The issue should remain open until all four PRs merge and parity is revalidated on main.