🔧 /feature Phase 0.0: fetch the issue body + aged-scope re-validation

Add `body` to the Phase 0.0 `gh issue view --json` field list and read it as the primary scope source. Add an aged-scope gate: when the issue is old (~7 days rule of thumb) or its body references files/symbols that no longer match the codebase, re-validate the scope against the current code and present the drift to the user before implementing.

Created via /dev:issue
