Unified Tooltip component for consolidating tooltip usage

[jabrailkhalil]

Closes #1482

Consolidates the tooltip usage across CatColab into one unified Tooltip component in ui-components.

Changes

• New Tooltip component wrapping corvu's tooltip, with the standard tooltip-content styling and options for placement, focus/hover behaviour, and custom content classes.
• IconButton now uses the unified Tooltip instead of embedding corvu directly (no behaviour change).
• The document picker's popup was migrated to the same component with its original placement and classes preserved.
• Tooltip styles moved from icon_button.css into a dedicated tooltip.css.
• New Storybook stories with interaction tests: hover, focus, rich content, placement, custom trigger (anchor), and custom content classes.

Verification

• pnpm --filter ./packages/ui-components test: 220/220 pass (including the 7 new Tooltip interaction tests, run headless in Chromium via vitest browser).
• ui-components ci (tcm, tsc, oxlint --deny-warnings, oxfmt --check, stylelint) clean; frontend oxlint/oxfmt/stylelint clean.
• Storybook production build succeeds (storybook build); the UI Components preview will be deployed to Netlify.

Follow-up candidates (kept out of this PR to keep it focused): the rich text editor's CSS data-tooltip buttons and remaining native title attributes.

[jabrailkhalil]

The CI workflows for the current head 9d46435857 are waiting for contributor workflow approval (action_required): ui-components-tests, ci, build. Could a maintainer approve the pending runs when convenient? These runs have not executed their checks yet; I will address any failures once they run.

[epatters]

Thanks for your interest in contributing to CatColab.

Pursuant to our new and evolving LLM policy, all discourse in the dev process must be made by, and written by, humans. In particular, this precludes the possibility of wholly LLM-generated PRs, as this one appears to be.