fix: ensure dropdown width respects trigger size and truncates long option labels

[michaelmkraus]

Proposed changes

Fixes the dropdownWidth="auto" behavior in DBCustomSelect where the dropdown menu collapsed to its minimum width instead of sizing to content, and long option labels wrapped uncontrollably instead of being truncated.

Root cause (3 gaps identified):

• Missing CSS block: No &[data-width="auto"] selector existed in custom-select-dropdown.scss, so the dropdown had no defined inline-size and collapsed to min-inline-size.
• No trigger-width sync: handleFixedDropdown only synced width for full mode. When switching to position: fixed, the auto dropdown lost all reference to its trigger's width.
• No text truncation: List-item labels had no white-space: nowrap / text-overflow: ellipsis, causing multi-line wrapping in narrow dropdowns.

Changes:

• custom-select-dropdown.scss — Added &[data-width="auto"] { inline-size: max-content; }. The existing max-inline-size viewport guard prevents overflow.
• floating-components.ts — Set element.style.minInlineSize = ${width}px for auto mode so the dropdown is never narrower than its trigger.
• custom-select-list-item.scss — Added white-space: nowrap; overflow: hidden; text-overflow: ellipsis; on > label for single-line truncation.
• New showcase — dropdown-width-auto.example.lite.tsx with 4 edge-case scenarios (long text, wide trigger/short options, narrow trigger/long options, mixed lengths) to visually reproduce and regression-test the bug.

resolves #6250

Checklist

Code Quality

• I have reviewed my own code (self-review), including the screen- and snapshots
• I have reviewed my changes locally with an AI assistant (e.g. GitHub Copilot, Kiro, etc.)
• No hardcoded values, magic numbers, or debug code left in

Validation

• I have added/updated tests that cover my changes
• I have tested across all relevant frameworks (React, Angular, Vue) if applicable

General

• The PR title follows the conventional commits format (e.g. feat:, fix:, chore:), as in Git Commit Conventions
• If architecture, structure, or conventions changed inside a packages/* folder, the corresponding AGENTS.md has been updated

🔭🐙🐈 Test this branch here: https://design-system.deutschebahn.com/core-web/review/fix-custom-select-dropdown-wrapping

[changeset-bot]

🦋 Changeset detected

Latest commit: 7575d77

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@db-ux/core-components	Patch
@db-ux/ngx-core-components	Patch
@db-ux/react-core-components	Patch
@db-ux/wc-core-components	Patch
@db-ux/v-core-components	Patch
@db-ux/core-foundations	Patch
@db-ux/core-stylelint	Patch
@db-ux/core-migration	Patch
@db-ux/agent-cli	Patch
@db-ux/core-eslint-plugin	Patch
@db-ux/core-vite-plugin	Patch
@db-ux/core-postcss-plugin	Patch
@db-ux/mcp-server	Patch

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