[codex] Clarify sparse Fabric provenance guidance

[lutefd]

Summary

• Clarifies that Fabric session workflows should record causal provenance only at meaningful checkpoints with stable provider object IDs.
• Tightens the provenance skill so informed_by and implements relations stay sparse and are not inferred from available context.
• Updates the direction-recording skill to explicitly exclude provenance, exposure receipts, and 'I used this direction' facts from direction notes.
• Adds template regression checks for the provenance/direction boundary.

Rationale

Fabric Lens and similar visualizers need causal edges to exist, but those edges should not pollute direction. This change makes the agent-facing guidance more explicit: direction remains reusable project guidance, while exposure and causality belong in provenance relations.

Impact

Agents generated from these templates should be less likely to either skip meaningful causal receipts or incorrectly store provenance as direction. Existing users only see documentation/skill behavior changes.

Validation

• go test ./...
• git diff --check
• fabric sync reported no new relevant direction for the active visualizer/provenance thread.