#1 R1 spike: markdown+frontmatter deps decision

Context: DRAFT pins Rust + minimal deps but names are unconfirmed. Time-boxed spike before any render code. Tasks:

• Spike pulldown-cmark 0.13.4 on f0rge fixtures (issue.md, pr.md, wiki page): markdown->HTML, confirm escaping of <script>.
• Spike frontmatter: tiny --- split + serde_yaml on real .forge/issues/<uuid>/issue.md files (borrow ../f0rge/.forge). Confirm unknown-field tolerance + missing-field error naming file+field.
• Confirm RFC3339 parse approach (chrono vs hand-rolled) and JSON via serde_json.
• Output: docs/deps-decision.md (or wiki note) locking versions + fallback if a crate is rejected. Success rubric:
• Decision doc exists with pinned versions + why, deps total <= 5.
• Spike parses 20+ real f0rge fixture files with 0 panics; malformed file yields named error.
• No tokio/hyper needed: confirmed std-only path for later inbox work. Swarm: one Owlette/Owl, read-only, no repo code changes except decision doc.