fix(harness-ops): inventory parser reader's repair command is POSIX-only on Windows #5826

Problem

plugins/harness-ops/skills/inventory/scripts/parser_reader.py reports a broken parser install with one repair line built from rm -rf, mkdir -p, cp, && and POSIX single-quote escaping (shlex.quote). On Windows that line runs in neither cmd.exe nor Windows PowerShell 5.1, so a Windows user gets no usable recovery command exactly when the reader reports broken. The same gap was raised by Codex on the miro launcher in #5824 (#5824 (comment)), and the P1 implementer flagged it for this reader when #5793 shipped.

Fix

Build the repair command per platform: on sys.platform == "win32" emit a PowerShell form valid in 5.1 (; chaining with $ErrorActionPreference='Stop', Remove-Item -Recurse -Force, New-Item -ItemType Directory -Force, Copy-Item, npm ci --prefix ..., single quotes doubled); keep the POSIX form elsewhere. Align the wording in docs/conventions/on-demand-dependencies/README.md rule 3 if it names a shell.

Acceptance

• Tests cover both forms, including a path with a space and a single quote.
• The Windows form, pasted into Windows PowerShell 5.1, reinstalls the parser packages.

Related: #5640, #5793, #5752, #5824.