Add screenshot capture tool and dev setup docs

docs/dev.md

@@ -1,5 +1,7 @@
 # Local development
 
+Toolchain prerequisites: see [setup.md](setup.md).
+
 ## Run
 
     go run .
@@ -16,3 +18,4 @@ The server reads local data from `sampledata/`, mirroring the production Sheets
 - `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
+- `tools/screenshot` — dev-site page capture, see [screenshots.md](screenshots.md)

docs/plan.md

@@ -19,7 +19,7 @@
 - One command starts the local server.
 - Templates, static assets, and content reload on change without restarting the server.
 - A local data mode serves generated, non-production sample data so contributors never need real community data to develop or test.
-- A documented screenshot mechanism captures pages from the local dev server, so agents (and humans) can verify visual changes. See `docs/screenshots.md` once it exists.
+- A documented screenshot mechanism captures pages from the local dev server, so agents (and humans) can verify visual changes. See `docs/screenshots.md`.
 
 ## Directory app
 

docs/screenshots.md

@@ -0,0 +1,27 @@
+# Screenshots
+
+`tools/screenshot` captures pages from the local dev server as PNGs, so humans and agents can verify visual changes. It drives a locally installed Chrome (or Chromium) headless via chromedp; no other browser tooling is required.
+
+## Usage
+
+With the server running:
+
+    go run ./tools/screenshot -url http://localhost:8080/directory/ -out screenshots/directory.png -wait header
+
+Flags:
+
+- `-url` — page to capture (default `http://localhost:8080/directory/`)
+- `-out` — output PNG path (default `screenshots/capture.png`); `screenshots/` is gitignored
+- `-wait` — CSS selector that must be visible before capture (default `body`); pass a selector the page's JavaScript renders (for example `.card`) to capture after data loads
+
+The capture is a full-page screenshot at a 1280×800 viewport.
+
+## Agent recipe
+
+One self-contained command that starts the server, captures, and shuts down:
+
+    go run . &
+    go run ./tools/screenshot -out screenshots/directory.png -wait header
+    kill $(lsof -ti :8080)
+
+Then read `screenshots/directory.png` to inspect the result.

docs/setup.md

@@ -0,0 +1,11 @@
+# Dev environment setup
+
+Development happens on macOS. Two Homebrew installs, and everything in `docs/dev.md` and `docs/screenshots.md` works:
+
+    brew install go
+    brew install --cask google-chrome
+
+- **Go** 1.26 or later — builds and runs the server and all tooling (`go run`, `go vet`).
+- **Google Chrome** — launched headless by the screenshot tool; never needs to be opened by hand. The tool finds it in its standard install location automatically.
+
+No Node, no Docker, and no cloud credentials are needed for local development.