Add env var fallback for KiBot text variables

- rev/rev_pcb: Use KIBOT_VAR_rev if set, else git describe
- name: Use KIBOT_VAR_name if set, else extract from filename

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

configs/pos.kibot.yaml

@@ -10,3 +10,8 @@ preflight:
   erc: false
   update_xml: false
   drc: false
+  set_text_variables:
+    - name: 'rev'
+      command: 'cat $CI_PROJECT_DIR/.version 2>/dev/null || cat .version 2>/dev/null || git describe --tags 2>/dev/null || echo unknown'
+    - name: 'rev_pcb'
+      command: 'cat $CI_PROJECT_DIR/.version 2>/dev/null || cat .version 2>/dev/null || git describe --tags 2>/dev/null || echo unknown'