docs: document Admin UI build step for contributors

Add the required `make build-ui` (or `npm ci && npm run vite:build`)
step to README.md, AGENTS.md, and docs/docs/development/building.md
so contributors know to build the Admin UI bundle after cloning.

Signed-off-by: Anna Effort <anna.effort@datastax.com>
Signed-off-by: Mihai Criveti <crivetimihai@gmail.com>

Author: a-effort

AGENTS.md

@@ -48,8 +48,9 @@ llms/                       # End-user LLM guidance (not for code agents)
 ```bash
 cp .env.example .env && make install-dev check-env    # Complete setup
 make venv                          # Create virtual environment with uv
-make install-dev                   # Install with dev dependencies
+make install-dev                   # Install with dev dependencies (includes build-ui)
 make check-env                     # Verify .env against .env.example
+make build-ui                      # Rebuild Admin UI JS bundle (requires npm)
 ```
 
 ### Development

README.md

@@ -655,7 +655,7 @@ For detailed setup, workflows, and GitHub Codespaces instructions, see **[Develo
 ## Installation
 
 ```bash
-make venv install          # create .venv + install deps
+make venv install-dev      # create .venv + install deps + build Admin UI
 make serve                 # gunicorn on :4444
 ```
 

docs/docs/development/building.md

@@ -101,6 +101,29 @@ The Admin UI uses plain JavaScript (not TypeScript). Frontend tooling requires N
 npm install        # install frontend dev dependencies
 ```
 
+### Building the Admin UI Bundle
+
+The Admin UI JavaScript is bundled with Vite. The bundle is not committed to the repository — it is built locally during `make install-dev` (which calls `make build-ui`). Rebuild after any changes to files under `mcpgateway/admin_ui/`.
+
+```bash
+make build-ui          # build mcpgateway/static/bundle-<hash>.js (requires npm)
+```
+
+Or manually:
+
+```bash
+npm ci                 # install dependencies from lockfile (if not already done)
+npm run vite:build     # produce mcpgateway/static/bundle-<hash>.js
+```
+
+The server reads `mcpgateway/static/.vite/manifest.json` at startup to locate the hashed bundle filename.
+
+For iterative development you can use watch mode:
+
+```bash
+npx vite build --watch
+```
+
 ### Linting & Formatting
 
 ```bash