Harvest: --paths-only and --dry-run flags on iikit-core scripts

[jbaruch]

Status: Tier 2

Upstream spec-kit added two flags to its core scripts (commits 3227b966 #2672, b44ffc01 #1998):

• check-prerequisites.sh --paths-only returns paths without validating a feature branch (works on non-feature branches)
• create-new-feature --dry-run previews without writing

What we'd build

Add equivalent flags to iikit-core/scripts/bash/:

• check-prerequisites.sh --paths-only — emit paths without the feature-branch gate
• create-new-feature.sh --dry-run — print what would be created without writing
• (and their .ps1 mirrors)

Why it matters

• CI dry-runs: validate IIKit project structure without side effects
• Worktree isolation: lets us run IIKit from main for read-only inspection without tripping the feature-branch validator (relevant to the agent-worktree-isolation rule)
• Doctor: feeds the planned /iikit-core doctor (Harvest: /iikit-core doctor — health diagnostics for project state #74) with structured path data

Evidence

• Upstream commits: 3227b966 (#2672), b44ffc01 (#1998)

Cost

Small — two flags in two scripts (plus PowerShell mirrors).

Sequencing

Tier 2.

[jbaruch]

Shipped in PR #89 → merged as 9b1b255.