Pin Python version to <3.14 for local dev compatibility

pydantic-core's Rust extension (via PyO3) doesn't support Python 3.14 yet.
Add .python-version (3.11, matching Dockerfile) so pyenv/uv auto-select a
compatible version, and tighten requires-python to fail fast with a clear
error instead of a cryptic Rust build failure.

https://claude.ai/code/session_01EGBMur51izertyiu7msWPQ

.python-version

@@ -0,0 +1 @@
+3.11

pyproject.toml

@@ -2,7 +2,7 @@
 name = "videoguidemaker"
 version = "0.1.0"
 description = "Generate WCAG 2.2 AA-ready HTML study guides from instructional videos"
-requires-python = ">=3.10"
+requires-python = ">=3.10,<3.14"
 dependencies = [
     "fastapi>=0.115",
     "uvicorn[standard]>=0.32",