fix: tab highlight reactivity, cleanup docs and build scripts

- Fix tab highlight not updating visually — switch from class={tabClass()}
  to Svelte's class:active directive for proper reactive class binding
- Rewrite README.md with full project structure, architecture, build guide
- Rewrite build.sh to build both GUI and server, output to build/
- Add scripts/build.sh for granular builds (gui/server/all)
- Add build/, frontend-dist/, and test vault dirs to .gitignore
- Remove stale binaries from project root
- Update AGENTS.md session summary

scripts/build.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+set -e
+
+# Individual build scripts
+
+build_gui() {
+  echo "==> Building GUI binary..."
+
+  # Build frontend
+  cd frontend && npm run build && cd ..
+
+  # Copy frontend dist to Wails embed directory
+  cp -r frontend/dist/* cmd/verstak-gui/frontend-dist/
+
+  # Build Go binary with Wails v2
+  # Tags: webkit2_41 required for WebKitGTK 2.41+, desktop/production for Wails
+  go build -tags "webkit2_41 desktop production" -ldflags="-s -w" -o build/verstak-gui-linux-amd64 ./cmd/verstak-gui/
+
+  echo "==> GUI binary: build/verstak-gui-linux-amd64"
+}
+
+build_server() {
+  echo "==> Building server binary..."
+  go build -ldflags="-s -w" -o build/verstak-server-linux-amd64 ./cmd/verstak-server/
+  echo "==> Server binary: build/verstak-server-linux-amd64"
+}
+
+build_all() {
+  mkdir -p build
+  build_gui
+  build_server
+  echo "==> All binaries built."
+  ls -lh build/
+}
+
+case "${1:-all}" in
+  gui)    build_gui ;;
+  server) build_server ;;
+  all)    build_all ;;
+  *)
+    echo "Usage: $0 [gui|server|all]"
+    exit 1
+    ;;
+esac