I have been learning chords & rhythm for 6 months or so; but all I really want to learn is to play melody for popular songs that I like. All beginner guitar books teach chords.
I tried looking for "Lead Guitar" books and they pretty much teach pentatonic scales and some blues riffs.

Q1. Is it correct that to be able to learn to play lead/melody, I need to practice using scales & modes books as technique builder?
Q2. Is there any book/online course that teaches melody playing or lead guitar which isn't just blues stuff?
Q3. Does "Lead Guitar" mean same as melody playing?

1. No. It might be useful to know scales and modes, depending on what goals you are after as a musician. But many players in the past and present has learned to play simply by imitating stuff they have heard on records and improving their ear. You will learn scales that way as well, you just won't have the name for it.

2. There are tons of books and videos on playing guitar. There are sites like LickLibrary, Jamplay, Guitarmasterclass etc that offers lessons, and there is an infinite amount of private teachers on the web for any style you'd like to learn.

3. Lead guitar is (in my opinion) a unnecessary term. People sometime put themselves into categories as "rhythm" or "lead" guitarists because of various reasons. Most of the time i see it as them being lazy and not working on both aspects of their playing. I simply call myself a guitarist, and i will do what the situation calls for. If that means being more of a rhythmic component in the band, so be it. If it means being a soloist, so be it. If it means providing harmony, so be it.
Fusion and jazz musician, a fan of most music.

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Quote by Chick Corea
"Only play what you hear. If you don't hear anything, don't play anything."
you dont actually need to learn a lot of music theory on harmony and chord notation to make good lead solos/melody. Music theory is mostly an agreed upon understanding/guidelines of tonality and how good certain notes transition into chords and how chords transition into other chords and etc. What is absolutely important IMO is learning fretboard patterns, then music theory. knowing your fretboard is an extremely strong advantage which seperates the good vs bad guitarists. Knowing these patterns then learning the theory will make you go "oh, that makes sense" or "oh, so that does connect" in a lot of occasions

what i used to do before learning music theory is jam to a certain part of the song on repeat and record a bunch of takes for solos. if one take has something i like and another has something i also like, i use the first half of the first take and the second half of the second take/viceversa and rehearse those as one solo, then record.