docs(powershell-lsp): rewrite ROADMAP Section 4 into a four-horizon forward ladder (000116)

[manderse21]

Dispatch 000116 (powershell-lsp). Doc-only, no version bump, one file.

Rewrites Section 4 of ROADMAP-powershell-lsp.md from "Open work (live dispatch state)" into a sequenced four-horizon forward ladder -- so the roadmap has an unblocked-now horizon rather than a set of parked lanes:

• H0 Immediate tactical (unblocked now; gated only on accept)
• H1 Near-term tactical (survey-first, one slice per dispatch)
• H2 Enterprise hardening (parallel track; adoption-gating)
• H3 Strategic / what-if (the bets; not committed work)

Each build item names its gate and its output. Folds in the dispositioned 10-item external-feedback set (as a disposition table) and the enterprise-hardening track.

Verification (this session, against disk / live GitHub):

• Every "already shipped" reference traced to CHANGELOG.md: formatOnEdit=apply + moduleAwareness (v1.23.0); project-intelligence slice 1, closed-loop correction, SARIF standalone (v1.19.0); AI-era rule pack CLOSED (v1.22.0); base curation (v1.21.1).
• 000054 (PL-2 latency baseline) confirmed abandoned via dispatch list.
• Upstream issue states re-checked live via gh: anthropics/claude-plugins-official#1359 OPEN; anthropics/claude-code#66987 OPEN; anthropics/claude-code#73961 OPEN.
• No external-feedback document exists on disk, so the embedded dispositions are used as-is.

Scope: only Section 4 changed; Sections 1-3 and 5-7 are byte-stable (no Lane/Phase cross-references existed to update). ASCII-only, LF, no-BOM. Diff: +98/-26, one file.

HELD for Mike's merge.

https://claude.ai/code/session_01J7p9GGXumBv6pJhQzQ3e6X