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

[dgenio]

Why

agent-kernel already describes the correct behavior — raw output is always firewalled into a bounded Frame. This aligns with weaver-spec BOUNDARIES.md and Invariants I-01, I-02. However, there is no formal declaration of spec compatibility, and no automated validation.

Formalizing this:

1. Makes the alignment visible and discoverable
2. Enables the weaver-spec compatibility matrix to be filled in
3. Ensures future changes don't silently break compliance

Acceptance Criteria

• README section: "Weaver Spec Compatibility: v0.1.0" stating which invariants agent-kernel satisfies (at minimum I-01, I-02, I-06)
• 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 agent-kernel's tested version

Dependencies

• Conformance suite: dgenio/weaver-spec#4

Context

Part of Milestone E0 — Connect + Align Boundaries.