Upgrade CI, Docker, and demos to Python 3.14

Update all GitHub Actions workflows and Dockerfiles to use Python 3.14
as the default version. Remove the upper bound on requires-python in
model_choice_with_test_harness to allow 3.14+. The CLI's
requires-python stays at >=3.10 for broad compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Install uv
         run: curl -LsSf https://astral.sh/uv/install.sh | sh
@@ -103,7 +103,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Download plano image
         uses: actions/download-artifact@v4
@@ -189,7 +189,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Install uv
         uses: astral-sh/setup-uv@v5
@@ -239,7 +239,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Install uv
         uses: astral-sh/setup-uv@v5
@@ -289,7 +289,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Install uv
         uses: astral-sh/setup-uv@v5
@@ -389,7 +389,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Download plano image
         uses: actions/download-artifact@v4
@@ -441,7 +441,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Download plano image
         uses: actions/download-artifact@v4

.github/workflows/publish-pypi.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v4
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Install uv
         uses: astral-sh/setup-uv@v4