Surgical editing

Search before editing and refuse ambiguous changes.

Search before editing and refuse ambiguous changes:

arka surgical-edit find src/app.py "target function"
arka surgical-edit edit src/app.py "old text" "new text" --yes
arka surgical-edit edit src/app.py "old text" "new text" --all --yes

Arka prints matching lines first, requires a unique match by default, creates a .bak backup, and makes no change when the keyword is missing or ambiguous. Natural language requests are supported when the file and old/new text are quoted clearly.