Shared checklist blocks that many tasks can reference #370

Problem

Agent-ready tasks repeat the same project rules and build/compile checklist. When a rule changes (e.g. '.meta files are git-ignored' became 'tracked'), 41 task texts are outdated at once; the only fix is overriding them via the project instructions and hoping agents weigh them correctly.

Proposal

Reusable blocks (e.g. a page or snippet item) that tasks reference by number and that item_get/recall inline or link, so a rule is changed in one place. Alternatively: task content can mark a section as 'inherited from #N'.

Evidence

Hyperion Drift 2026-09-27: after fixing .gitignore every Epic G task still said meta files are git-ignored.