fix(watch-later): make thumbnail WL button actually add videos

[neelavradutta]

issue id - #4187
bug name - watch later

Summary

Watch Later thumbnail button showed up but did not add videos to the WL playlist. Native click could hit the wrong overlay control, and the Innertube fallback lacked auth headers YouTube expects when logged in (notably on Safari).

• Match only real Watch Later controls (exclude our button; no random toggle fallback)
• Innertube add uses SAPISIDHASH + YouTube client headers
• Keep optimistic UI state only after native click attempt

Test plan

• Enable General → Watch Later buttons → always
• Stay logged in to YouTube
• Click the clock on a thumbnail → button turns added / video appears in playlist?list=WL
• Retry on Safari if available

Thank you

[ImprovedTube2]

thank you guys! @neelavradutta @harshjainnn
the extension did not use innertube yet. (however https://github.com/LuanRT/YouTube.js/ is all about it. should both projects merge?)

• please make sure this does not break the functionality for anybody yet. (idk if it broke for everybody or just part of users)

i just merged #4203 still before i saw #4208
should i undo this?

( Reviewing PRs quickly in 2026, i tend to wish the code came classified line by line

.	tested	LLM
yes
no

)

thanks