workspace skeleton: UAPF 2.2.0 layout + L0 enterprise index

Step 1 of the vk-gramatvediba build.

- normative folder structure: enterprise/ , domains/ , processes/
- enterprise/enterprise.yaml — L0 enterprise index (validates against
  the UAPF 2.2.0 enterprise-index schema; packages[] filled in later steps)
- README and docs/conventions.md — VK function-group to UAPF level
  mapping, composition rule, transcription-fidelity policy
- CODEOWNERS placeholder and .gitignore (built .uapf archives excluded)

Targets UAPF specification v2.2.0.

enterprise/enterprise.yaml

@@ -0,0 +1,11 @@
+kind: uapf.enterprise.index
+level: 0
+enterprise:
+  id: vk.gramatvediba
+  name: Valsts Kase — Grāmatvedības uzskaite
+  description: >-
+    Enterprise index for the Valsts Kase / Vienotais pakalpojumu centrs (VPC)
+    accounting workspace — a UAPF transcription of the six published accounting
+    function groups (FG1–FG6). Domain and process packages are registered here
+    as they are added to the workspace.
+packages: []