[tabs] Add generic value typing to Root

[lyzno1]

Fixes #5516.

Makes Tabs.Root generic over its value type so value, defaultValue, and onValueChange stay aligned through inference or an explicit generic.

Keeps Tabs.Tab, Tabs.Panel, and the internal context permissive. onValueChange remains nullable to match the existing automatic fallback behavior.

• I have followed (at least) the PR section of the contributing guide.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@5568
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@5568
  

commit: edeb696

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	0B(0.00%)	0B(0.00%)

Details of bundle changes

Performance

Total duration: 1,516.81 ms 🔺+442.36 ms^(+41.2%) | Renders: 76 ⁽⁺⁰⁾ | Paint: 2,454.92 ms 🔺+720.36 ms^(+41.5%)

Test	Duration	Renders
Tabs mount (200 instances)	302.18 ms 🔺+97.90 ms(+47.9%)	3 (+0)
Select mount (200 instances)	193.22 ms 🔺+68.52 ms(+54.9%)	3 (+0)
Menu mount (300 instances)	128.53 ms 🔺+56.71 ms(+78.9%)	1 (+0)
Slider mount (300 instances)	163.97 ms 🔺+53.73 ms(+48.7%)	2 (+0)
Scroll Area mount (300 instances)	99.45 ms 🔺+41.79 ms(+72.5%)	3 (+0)

…and 8 more (+2 within noise) — details

Metric alarms

Test	Metric	Change
Tabs mount (200 instances)	bench:paint	🔺 +122.19 ms
Select mount (200 instances)	bench:paint	🔺 +92.89 ms
Menu mount (300 instances)	bench:paint	🔺 +83.82 ms
Slider mount (300 instances)	bench:paint	🔺 +94.44 ms
Scroll Area mount (300 instances)	bench:paint	🔺 +53.54 ms

…and 13 more metric alarms — details

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Check out the code infra dashboard for more information about this PR.

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