fix: match daemon process flags exactly

[brannn]

Summary

• replace substring matching for daemon command-line flag verification with exact token-boundary matching
• move the command-line matcher into shared process arg helpers
• add parser tests covering separate and equals flag forms plus prefix mismatches

Test Plan

• go test ./cmd/threadmark -run TestCommandLineHasFlagValue -count=1
• go test ./cmd/threadmark -count=1
• GOOS=darwin GOARCH=amd64 go test -c ./cmd/threadmark -o /tmp/threadmark-darwin.test
• go test ./...
• git diff --check