Adopt designed front matter: typed, with staleness on plans

Replaces `type: default` — one value across every document, read by nothing.
Types are now reference, guidelines, plan and report; plans carry status and
updated, reports carry date. Convention documented in project-yukart REPOS.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

README.md

@@ -1,5 +1,5 @@
 ---
-type: default
+type: reference
 ---
 # Jetson Orin Nano environment setup for doing things in a car
 

docs/BOM.md

@@ -1,5 +1,5 @@
 ---
-type: default
+type: reference
 ---
 # Bill of Materials
 

docs/GUIDELINES.md

@@ -1,5 +1,5 @@
 ---
-type: default
+type: guidelines
 ---
 # Orin Nano env setup Guidelines
 

docs/impl/reports/PCAN-SETUP.md

@@ -1,3 +1,7 @@
+---
+type: report
+date: 2026-08-04
+---
 # PCAN-USB Adapter Setup on Jetson Orin Nano
 
 ## Hardware