fix: Remove YAML usage, standardize on JSON/TOML

- Delete 5 legacy .formula.yaml files (have .toml replacements)
- Remove unused FileConfigYAML constant
- Add TODO for beads config.yaml → config.json migration (bd-10wg)
- Update docs to use JSON examples instead of yaml code blocks
- Change plugin frontmatter from YAML to TOML in docs
- Add .toml to code file detection in branch_check.go

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/templates/roles/witness.md.tmpl

@@ -274,23 +274,16 @@ This sends handoff mail, respawns fresh. Your next instance picks up from your h
 
 Your handoff state is tracked in a pinned bead: `witness Handoff`
 
-```yaml
-# Find with: bd list | grep "witness Handoff"
-attached_molecule: mol-witness-patrol
-attached_at: 2025-12-24T10:00:00Z
-
-# Nudge escalation tracking
-nudges:
-  toast:
-    count: 2
-    last: "2025-12-24T10:30:00Z"
-  ace:
-    count: 0
-    last: null
-
-# Polecats queued for cleanup
-pending_cleanup:
-  - nux  # received POLECAT_DONE, awaiting verification
+```json
+{
+  "attached_molecule": "mol-witness-patrol",
+  "attached_at": "2025-12-24T10:00:00Z",
+  "nudges": {
+    "toast": {"count": 2, "last": "2025-12-24T10:30:00Z"},
+    "ace": {"count": 0, "last": null}
+  },
+  "pending_cleanup": ["nux"]
+}
 ```
 
 On startup, check for attached work: