feat(preview): add inline code copy action

[happykawayigt]

Summary

• add a compact copy action to inline code that appears on hover or keyboard focus
• reuse shared clipboard and feedback behavior for inline and fenced code
• prevent the copy action from activating surrounding links or click handlers
• cover successful copies, failures, temporary feedback, and event isolation

Validation

• targeted preview tests: 8 passed
• npm run build
• npm run lint
• git diff --check
• full npm test -- --run: 284 passed, 1 failed in HotKeyHandler.test.tsx; the same full-suite-only failure reproduces on a clean latest main (280 passed, 1 failed), while that test passes in isolation

Fixes #1358

AI assistance: Codex was used to help investigate, implement, and test this change.

[perber]

@happykawayigt Thanks, have you checked the UI. A short manual test?

[perber]

Could you rebase.

[perber]

I checked, the design it looks different to the codeblock, the tooltip, ...
Could you fix it?

[happykawayigt]

Fixed in 2a49d11. I aligned the inline control with the fenced-code control by reusing TooltipWrapper and the same border, background, foreground, and hover styling while keeping the compact inline size.

Manual UI check: I rendered inline and fenced code together through the real MarkdownPreview, verified the inline control appears on hover, the tooltip says “Copy code”, and clicking changes the accessible label to “Code copied”. The targeted preview tests (8), lint, and build all pass.

[perber]

Hi @happykawayigt,

Thanks again! It looks already pretty good, but I think it is better, when no padding is on the right side.
The inline code is position: relative and the click button is absolute positioned as in the code block.

As the copy button is only visible on hover I think it is ok to overlap the content with the button.

[perber]

see above comment

[perber]

Ran the copy button through a design-consistency check against the app's existing patterns (fenced-code copy button, headline-anchor hover-reveal) and pushed a small follow-up commit (ceaa93d1):

• border-radius: 0.125rem → var(--radius-sm) — 0.125rem isn't on the app's radius scale (--radius-sm: 0.25rem / --radius-md: 0.375rem / --radius-lg: 0.5rem); next to the fenced-code button's clearly rounded corners the inline one read as noticeably sharper.
• Added transition: opacity 200ms — the only other hover-reveal control in the app (headline anchors) fades in with transition-opacity duration-200; the inline copy button was popping in/out instantly.

Left the icon-overlapping-text-on-hover behavior as-is (not adding extra margin/padding for it). Everything else — clipboard/toast reuse, color tokens, icons — already matched house conventions well.

(Also ran into a pre-existing, unrelated bug while testing — inline code spans rendering with literal backticks — confirmed it reproduces on main too, so it's not from this PR. Logged separately, not something to fix here.)