Scaffold repo: docs layout, guidelines and initial plan

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

docs/GUIDELINES.md

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+---
+type: default
+---
+# Map minting guidelines
+
+## 1. Artifacts are never committed
+- Routing tiles and basemaps are large binaries rebuilt from upstream. This repo
+  holds the scripts that produce them and a report of the procedure, nothing else.  
+- Every build records the source PBF's date. An artifact whose provenance is
+  unknown is an artifact to rebuild.
+
+## 2. Build the admin database first
+- `valhalla_build_admins` is what determines driving side, and it is a separate
+  step *before* the tile build.  
+- Skip it and Valhalla routes and narrates as though Japan drove on the right.
+
+## 3. Tiles ship as a directory, not a tar
+- Once for RAM on an 8 GB board, once because `rsync` deltas a tree of changed
+  files where a multi-gigabyte tar forces a full checksum at both ends.
+
+## 4. To be added