Add server skeleton with directory app and local dev loop

docs/dev.md

@@ -0,0 +1,18 @@
+# Local development
+
+## Run
+
+    go run .
+
+The server listens on http://localhost:8080 (override with `PORT`). Templates, static assets, and sample data are read from disk on every request — edit a file and refresh the browser; no restart needed.
+
+## Local data
+
+The server reads local data from `sampledata/`, mirroring the production Sheets layout: one directory per app, one CSV file per table, first row is the schema. It goes through the same data-source interface production backends implement, so app code never knows which backend it is talking to.
+
+## Layout
+
+- `main.go` — server entry point and app routing
+- `internal/data` — data source interface and the CSV sample-data implementation
+- `internal/directory` — directory app handlers
+- `web/directory` — directory app page templates and static assets