⬆️ Update dependencies and configure Dependabot for conda ecosystem

- Update anaconda: 2025.06 → 2025.12
- Update quantecon-book-theme: 0.14.0 → 0.15.1
- Update sphinxext-rediraffe: 0.2.7 → 0.3.0
- Pin jupyter-book to >=1.0.4post1,<2.0
- Configure Dependabot to use conda ecosystem for environment.yml
- Add ignore rule for jupyter-book versions >=2.0

Author: mmcky

.github/dependabot.yml

@@ -11,3 +11,13 @@ updates:
       prefix: ⬆️
     schedule:
       interval: weekly
+
+  - package-ecosystem: "conda"
+    directory: "/"
+    commit-message:
+      prefix: ⬆️
+    schedule:
+      interval: weekly
+    ignore:
+      - dependency-name: "jupyter-book"
+        versions: [">=2.0"]

environment.yml

@@ -3,13 +3,13 @@ channels:
   - default
 dependencies:
   - python=3.13
-  - anaconda=2025.06
+  - anaconda=2025.12
   - pip
   - pip:
-    - jupyter-book==1.0.4post1
-    - quantecon-book-theme==0.14.0
+    - jupyter-book>=1.0.4post1,<2.0
+    - quantecon-book-theme==0.15.1
     - sphinx-tojupyter==0.6.0
-    - sphinxext-rediraffe==0.2.7
+    - sphinxext-rediraffe==0.3.0
     - sphinx-exercise==1.2.1
     - sphinxcontrib-youtube==1.4.1
     - sphinx-togglebutton==0.3.2