fix: correct module path to github.com/TNG/oh-my-agentic-coder

[CodingTil]

Issue: Closes #98 Finding 1
#99 does not truly solve this finding, it only mitigates it.

What

• Corrects the go module path to the actual git remote
• This enables installation via go install github.com/TNG/oh-my-agentic-coder/cmd/omac@latest

Why

• Simple installation option
• Good practice to point the go module path to the actual git remote

How

• Renamed all findings of github.com/tngtech/oh-my-agentic-coder to github.com/TNG/oh-my-agentic-coder
• Adjusted documentation in docs/INSTALLATION.md

Verification

• go test ./...
• go vet ./...
• gofmt -l .
• go build cmd/omac/main.go

Follow-up

-/-

[nhuelstng]

this just needs another sweep since stuff changed and a rebase but then it can go in