Add an optional data-governance layer (authoritative source, sensitivity, provenance)

[dubedad]

Add an optional data-governance layer

What this adds

One optional reference doc — references/data-governance.md — plus a single pointer line in SKILL.md's References list. Nothing becomes mandatory. No form requires it; workspaces that don't hold sensitive data ignore it at zero cost.

It formalizes three things ICM already reaches for informally, for the case where a workspace holds shared, regulated, or sensitive data (a team brain, client/personal records, anything with a compliance obligation):

1. Authoritative source — makes invariant 8's "one home per fact" a declared source of truth (source_of_truth: frontmatter + an optional _glossary/), so a reader can tell the master from a mirror and the walk-test dedup check has an answer to "which is real?"
2. Sensitivity classification — generalizes the knowledge-bundle access_tier idea to any form. Since ICM's defining move is one agent walks the whole workspace, what the agent may read/quote/send is a first-class concern. Adds a walk-test question: walking cold, could I read or exfiltrate something above its tier?
3. Output provenance — source:/generated_from: frontmatter on factory outputs, turning invariant 9 ("filesystem is the state machine") into an auditable one: status becomes not just "what exists" but "what produced it."

Why it fits rather than bloats

• Opt-in, not a new invariant. Three frontmatter conventions and one folder, applied only when data sensitivity earns it. Same "drop any field nobody queries" guardrail as the rest of ICM.
• Extends seeds already in the skill — access_tier, "one home per fact," _meta/schema.md — rather than importing an external framework wholesale.
• Complements, doesn't overlap, the reference-integrity gate: that PR protects moves; this protects meaning, access, and origin.

Drawn from DAMA-DMBOK (metadata/glossary, data security & privacy classification, master/reference-data authoritative source), reduced to the smallest form that serves a one-agent folder workspace.

Best reviewed after the reference-integrity gate PR, which this references.