docs: fix outdated github.com/google/mediapipe URLs and typo

[ambicuity]

Description

This PR updates all references from the old repository URL (github.com/google/mediapipe) to the current URL (github.com/google-ai-edge/mediapipe) across 30 documentation and source files. It also fixes a duplicate-word typo (by by → by) in README.md and docs/index.md.

Changes

1. Outdated GitHub org URLs (30 files, 117 instances)

All occurrences of github.com/google/mediapipe have been updated to github.com/google-ai-edge/mediapipe in:

• Root files: README.md, setup.py
• Docs: docs/index.md, docs/getting_started/*.md, docs/solutions/*.md, docs/tools/visualizer.md, docs/build_*_api_docs.py
• Issue templates: .github/ISSUE_TEMPLATE/19-other-issues.md
• Example READMEs: mediapipe/examples/desktop/autoflip/README.md, mediapipe/examples/desktop/youtube8m/README.md
• Python source (comments/docstrings): mediapipe/tasks/python/metadata/*.py, mediapipe/tasks/python/vision/*.py, mediapipe/model_maker/setup.py, mediapipe/model_maker/python/vision/gesture_recognizer/metadata_writer.py

2. Typo fix

README.md line 30 and docs/index.md line 30: "by by checking" → "by checking"

Checklist

• Read contributing guidelines
• Read Code of Conduct
• This is a documentation fix (accepted PR type)
• Changes are minimal and safe (text-only URL and typo corrections)
• Verified locally: grep -rn 'github.com/google/mediapipe' returns 0 results after the fix