Feat v0.9.8 conditional routing SDK primitive

Promote workflow branch-rule evaluation to a generic Starlark
routing.evaluate(rules, data) module available to all extensions.
10 operators, first-match-wins, no permission gate. 8 new tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/STARLARK-REFERENCE.md

@@ -84,6 +84,24 @@ Returns `True` if the user has the permission, `False` otherwise (including
 when the user is not found). Resolves the user's groups and merges granted
 permissions — works for both kernel and extension-declared permissions.
 
+### routing
+
+Generic rule-based decision engine. Evaluates an ordered list of conditions
+against a data dict, returning the first matching rule's target string.
+
+```python
+result = routing.evaluate([
+    {"field": "priority", "op": "eq",  "value": "critical", "target": "escalation"},
+    {"field": "amount",   "op": "gt",  "value": 10000,      "target": "manager_review"},
+    {"field": "region",   "op": "in",  "value": ["EU", "UK"], "target": "gdpr_flow"},
+], stage_data)
+# Returns "escalation", "manager_review", "gdpr_flow", or None
+```
+
+Each rule is a dict with `field`, `op`, `value`, and `target`. Operators:
+`exists`, `not_exists`, `eq`, `neq`, `gt`, `lt`, `gte`, `lte`, `in`,
+`contains`. First-match-wins; returns `None` if no rule matches.
+
 ## Permission-gated modules
 
 These modules are only available if the package has the corresponding