Add Dependabot and link the org build-status page.

Author: barrybecker4

.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+  - package-ecosystem: "gradle"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    ignore:
+      # bb4-internal dependencies are already kept current by the CI cascade
+      # (repository_dispatch on every push) and the deliberate manual release
+      # process -- Dependabot opening PRs to bump these would just be
+      # redundant noise on top of a mechanism that already works.
+      - dependency-name: "com.barrybecker4:*"
+    open-pull-requests-limit: 10
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+

README.md

@@ -2,6 +2,8 @@
 
 [![CI](https://github.com/bb4/bb4-math/actions/workflows/ci.yml/badge.svg)](https://github.com/bb4/bb4-math/actions/workflows/ci.yml)
 
+📊 [Build status for all bb4 projects](https://github.com/bb4)
+
 Core math utilities used across bb4 projects: ranges and axis cut-points, interpolation, 1D functions, combinatorics, complex numbers, linear algebra helpers, and multi-dimensional arrays.
 
 ## Using it