BUGFIX: Move OWNERS to .github/CODEOWNERS to fix #3978

[chicks-net]

Summary

Fixes #3978

GitHub requires the CODEOWNERS file to be located in the .github/ directory (or repository root with that exact name) to function properly. This PR moves OWNERS to .github/CODEOWNERS and updates all references throughout the codebase.

Changes Made

• Renamed OWNERS → .github/CODEOWNERS
• Updated .gitattributes to reference the new location
• Updated build/generate/ownersFile.go to generate the file in the correct location
• Updated documentation in writing-providers.md to reference CODEOWNERS
• Added Tim as global owner

Test Plan

• Ran /bin/generate-all.sh to verify the generator creates the file in the new location
• Verified all file references were updated
• Checked that the file move preserves all content

% git grep OWNERS
.gitattributes:.github/CODEOWNERS eol=lf
build/generate/ownersFile.go:   file, err := os.Create(".github/CODEOWNERS")
documentation/advanced-features/writing-providers.md:  * `CODEOWNERS`

🤖 Generated with Claude Code

[tlimoncelli]

Hello friend!

Github is complaining that the people in CODEOWNERS do not have write permission. Each one gets an error such as:

Unknown owner on line 31: make sure @juliusrickert exists and has write access to the repository
providers/hostingde @juliusrickert

They don't have write permission because the current policy (from my employer) is that I have to approve any merge to main. Is there some other way to comply with the policy but give people write access?