feat(subagent): single routing resolver with persisted binding provenance

Model selection for a new subagent lived in planSpawn() and in the
config-section helper, and nothing recorded why a child was bound the way
it was, so a resumed child that kept an older model looked like a bug.

- resolveSubagentModelRoute() is the only authority that binds a model
  (inherit | default | pool | force, primary override, force rejects any
  explicit choice); resolveSubagentBinding() and the new
  SessionSubagentRoutingService both delegate to it. planSpawn() is a
  facade over the routing service and every plan carries
  RoutingProvenance: operation, profile/model source, policy mode and
  source, feature source, the ambient routingEnvironmentRevision and the
  request-level routeDecisionFingerprint.
- SubagentBindingProvenance is persisted once on the child (durable
  agent event + replayable state key) when it is created from a plan.
  Resume reads it back: modelSource/profileSource become resume-existing,
  the original revision is kept, and the caller's current revision is
  reported alongside, never written into the child.
- SubagentTaskInfo, the subagent.spawned event, REST /tasks, the WS
  roster and the session snapshot carry the provenance and the current
  revision; the protocol package and the web client map it into AppTask,
  DynamicWorkflowMember and the card rows.
- The Dynamic Workflow result writes durable <subagent> attributes
  (profile, model, thinking, provenance ids, started_at, completed_at)
  through the attribute escaper; the web parser reads them and older
  results without them still parse.

Author: elkaix

.changeset/subagent-routing-provenance.md

@@ -0,0 +1,5 @@
+---
+"@pymodel/pythinker-code": minor
+---
+
+Subagent tasks and Dynamic Workflow results now record the profile, model, and routing source of each subagent, and a resumed subagent keeps the binding it was created with.

apps/pythinker-code/dist-web/.web-bundle-manifest.json

@@ -1,4 +1,4 @@
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-  "sourceHash": "fd8373670e82925e4ab4b518d59498b2f1c18bfe495af7e88c946db7ce1e9b65",
+  "sourceHash": "e91c68ea648ad04740fb566377c1367d8118619bee85841fd8d2e9877e6c3c1d",
   "sourceFileCount": 405
 }