Replace logo with text-free icon for README and docs

Add icon.png (transparent background, trimmed) and rename the
original logo.png to icon_with_text.png for future use.

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

Author: laughingman7743

README.md

@@ -2,7 +2,7 @@
 
 <div align="center">
 
-<img src="docs/_static/logo.png" alt="PyAthena logo" width="200">
+<img src="docs/_static/icon.png" alt="PyAthena logo" width="200">
 
 | | |
 | --- | --- |

docs/_static/icon.png

@@ -162,7 +162,7 @@ def setup(app):
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
 html_theme = "furo"
-html_logo = "_static/logo.png"
+html_logo = "_static/icon.png"
 html_static_path = ["_static"]
 html_css_files = [
     "custom.css",