fix: use available Skill detail space without scrolling

[Lampese]

Related issue

Internal same-repository change; no linked issue.

Problem / pressure

Skill previews stop after five lines even when the detail pane has unused space. Descriptions should use the available height while the skill path stays visible and the pane remains stationary under wheel input.

Summary

• Give descriptions the remaining space between the fixed heading/metadata and bottom facts, including the path.
• Observe that space and show as many complete lines as fit, with an ellipsis for excess text.
• Keep the pane height controlled by the candidate list and clip overflow without scrolling.
• Add a long-list Storybook state, browser regression coverage, and bilingual decision notes.

Visual explanation

List-defined detail pane height
├─ Heading and scope                 fixed
├─ Description                       remaining height
│  └─ ResizeObserver → whole-line clamp → ellipsis
└─ Path and other facts               fixed at bottom

Wheel input does not scroll the detail pane.

Before / after

Before	After
Descriptions always stop after five lines.	Visible lines follow the actual remaining height.
The detail pane is a scroll container.	The pane stays stationary and its path remains visible.

Test plan

• NODE_ENV=test pnpm --filter @lody/components exec vitest run tests/mention-two-level-menu.test.tsx: 42 tests passed.
• pnpm --filter @lody/components exec playwright test tests/e2e/composer-mention-placement.spec.ts --grep 'skill descriptions use remaining height' --workers=1 --timeout=90000: passed for short and long lists at 12px, 14px, and 18px font settings.
• An isolated browser render of the actual detail component passed nine height/font combinations, checking title/path visibility, whole-line truncation, stable pane height, and no wheel scrolling.
• Captured and inspected the actual long-list Storybook preview.
• Component typechecking, pnpm format, scoped Oxfmt/Oxlint, and whitespace checks passed.
• pnpm check: all workspace typechecks, general lint, Effect lint, and 58 script tests passed. The local full-workspace test run was stopped after that; it did not complete. Use PR CI status for the remaining required test validation.
• Translation-key validation and all import, platform/process, presence, public-repository, local-writer, and Operation Inbox boundary checks passed.
• pnpm run docs check: six existing missing local Kimi/Pi paths in the bilingual subagent-events notes; no errors in the new note pair and no registered protected topics.

Context handoff

Internal same-repository branch. This PR changes the shared neutral candidate detail pane; Agent Roles continue using their separate detail component. The implementation decision and verification limits are recorded in .agents/notes/implemented/bug-fix/2026-10-20-mention-description-space.md and its Chinese counterpart.