Declare weaver-spec v0.1.0 compatibility + run conformance in CI

[dgenio]

Why

contextweaver has the boundary alignment issue (#144) and contract adapters (#143), but no formal declaration of spec compatibility and no CI gate to prevent future drift. This is the equivalent of agent-kernel#58 — without it, the weaver-spec compatibility matrix cannot be filled in for contextweaver.

Acceptance Criteria

• README section: "Weaver Spec Compatibility: v0.1.0" stating which invariants contextweaver satisfies (at minimum I-03, I-05)
• CI job that runs the weaver-spec conformance suite (once dgenio/weaver-spec#4 ships)
  • Can be a placeholder/stub step initially, activated when the conformance suite is published
• Update weaver-spec compatibility matrix with contextweaver's tested version
• Verify that contextweaver's RoutingDecision and ChoiceCard outputs validate against the JSON Schemas in contracts/json/

Dependencies

• Conformance suite: dgenio/weaver-spec#4
• Boundary alignment: dgenio/contextweaver#144 (should be resolved first)

Context

Part of Milestone E0 — Connect + Align Boundaries.