chore: add gitignore for mock-seed, roam CI workflow, formatting

- Add tools/mock-seed/ to .gitignore
- Add .github/workflows/roam.yml CI workflow
- Add .roam/fitness.yaml architectural fitness rules
- Rustfmt formatting fixes in show.rs and vector.rs
- Beads sync

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.roam/fitness.yaml

@@ -0,0 +1,11 @@
+rules:
+  - name: No circular imports in core
+    type: dependency
+    source: "src/**"
+    forbidden_target: "tests/**"
+    reason: "Production code should not import test modules"
+  - name: Complexity threshold
+    type: metric
+    metric: cognitive_complexity
+    threshold: 30
+    reason: "Functions above 30 cognitive complexity need refactoring"