build: M1 Dockerized development stack with PHP skeleton, config/logging, Tailwind assets, and wrappers

Implements MeshVault M1 (issues #6–11):

- Four-service Docker Compose stack (nginx, PHP-FPM 8.3, PostgreSQL 17, Node assets)
- Slim 4 + PHP-DI routing with escaped PHP views and production/dev error handling
- Immutable validated AppConfig with redacted diagnostics
- JSON stdout Monolog logging with job-scoped context
- Tailwind CSS v4 deterministic locked builds with template scanning
- POSIX and PowerShell dev wrappers (up/down/test/lint/assets/watch)
- Startup config validation fails before FPM serves as unprivileged www-data
- migrate/seed explicitly unavailable until M2 (#12); #10 remains open

Verified via clean-start acceptance on remote host (keith@192.168.2.23).

package.json

@@ -0,0 +1,12 @@
+{
+  "name": "meshvault-assets",
+  "private": true,
+  "scripts": {
+    "build": "tailwindcss -i ./assets/css/app.css -o ./public/build/app.css --minify",
+    "watch": "tailwindcss -i ./assets/css/app.css -o ./public/build/app.css --watch=always"
+  },
+  "devDependencies": {
+    "@tailwindcss/cli": "4.3.3",
+    "tailwindcss": "4.3.3"
+  }
+}