docs: add README.md navigation index

docs/README.md

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+# docs/
+
+## If you're Mischa
+
+**Doing something operational?** → [`guides/`](guides/)
+- [Posting a journal entry](guides/posting.md)
+- [Managing GPX files](guides/gpx-manager.md)
+- [Switching to a new trip](guides/trip-switching.md)
+- [Rebuilding local dev from scratch](guides/local-setup.md)
+
+**Checking project status?** → [`working/`](working/)
+- [Backlog](working/backlog.md)
+- [Production todo](working/production-todo.md)
+- [QA results](working/qa/results.md)
+
+**Design or architecture decisions?** → [`reference/`](reference/)
+- [Design system](reference/design-system.md)
+- [Architecture overview](reference/architecture.md)
+
+---
+
+## If you're Claude
+
+**Always-loaded project rules** → [`CLAUDE.md`](../CLAUDE.md) (repo root)
+
+**Active specs and plans** → [`working/specs/`](working/specs/) and [`working/plans/`](working/plans/)
+
+**Stable facts** → [`reference/`](reference/)
+
+**Raw research input** → [`research/`](research/)