Improve selective loader slider interaction

[diodiogod]

Improves the combined toggle/strength slider interaction in selective loader nodes.

What this changes:

• clicking the slider track jumps directly to that value
• dragging updates from the cursor's absolute position on the track
• slider clicks use a tighter Y-axis hit test so checkbox clicks still behave normally
• track clicks avoid accidentally toggling the block on/off

Why:

• testing block patterns is much faster when values can be set by direct track clicks
• the previous drag behavior could feel laggy because the value did not reliably follow the cursor position

Notes:

• this PR only changes the frontend interaction behavior in dynamic_inputs.js
• it does not include Krea 2 support or block weight text sync
• it complements Fix selective loader slider range mismatch #55, which fixes the separate min/max range metadata mismatch

Tested:

• frontend JS syntax check
• manual ComfyUI testing of click-to-jump and drag behavior

[diodiogod]

I see in another issue that you actually removed the click to jump on purpose, so you might not want this... For me it makes more sense. But feel free to close this if it's not aligned to your direction for it.