docs: scaffold trust/privacy extension repo from SEP-1913 carve

Carve the schema-bearing parts of SEP-1913 into three independent
experimental extensions, per @localden's "narrower first cut" ask and
the Tool Annotations IG's 2026-05-28 extension-first decision:

- io.modelcontextprotocol/trust-annotations (headline): narrow
  data-classification taxonomy (sensitive, untrusted) + open-ended
  evidenceRef pointer.
- io.modelcontextprotocol/action-metadata: carries forward SEP-2061
  (inputMetadata/returnMetadata/outcomes + requiresReview).
- io.modelcontextprotocol/ifc-fides: FIDES information-flow control as
  a profile of evidenceRef, not a wire root.

Adds repo meta (README, MAINTAINERS, CONTRIBUTING, LICENSE) and docs
(sep-disposition, intent-comment, decisions, open-questions,
trust-model, related-work). FIDES demoted to a profile; DataClass and
requiresReview rehomed; maliciousActivityHint and propagation parked on
the SEP-1913 umbrella. Citations index on public sources only.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

LICENSE

@@ -0,0 +1,11 @@
+Apache License
+Version 2.0, January 2004
+http://www.apache.org/licenses/
+
+Per SEP-2133, official MCP extensions are required to be available under the
+Apache 2.0 license. Experimental extensions in this repository follow the
+same convention so that contributions made here can flow into a future
+official extension repository without re-licensing.
+
+The full text of the Apache License, Version 2.0 is available at:
+https://www.apache.org/licenses/LICENSE-2.0