Keep h1 descenders above the highlight and fix light accent contrast

[RaviTejaKNTS]

Why

A light-mode check of 15 live pages found two bugs:

• Highlight covers letters: on titles that wrap, the green highlight on one line covered the bottoms of letters on the line above, in both themes. Examples: "everu" instead of "every" on /tld-directory on phones, and the "g" and "p" in "Zigbee compatible".
• Low contrast: green text on selected chips and buttons was at 4.37:1 in light mode, under the 4.5:1 minimum.

What changed

• h1 highlight: the highlight paints behind the title's other text (isolation: isolate on the h1, and z-index: -1 on the mark), so letters on the line above stay readable. A highlight that is a link or holds one keeps normal painting, so the link stays clickable.
• Light theme --color-accent-text: #3f7a00 becomes #3a7000, which gives 4.99:1 on --color-surface-2 and at least 4.5:1 on every light surface. Marker art keeps its own green.

Checks

• Sol reviewed it in two rounds. Round 1 found the link click problem, which is fixed, and round 2 passed.
• Checked in the browser on /tld-directory (390px, dark) and /zigbee-devices (1440px, light).
• npm run quality passes.

The light-mode check found no sideways scrolling and no console errors on any of the 15 pages.

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