fix(toolbar): multi-line toggleBlockquote support matching list toggle pattern

[alph-cmky]

Summary / 摘要

Make toggleBlockquote support multi-line selections, matching the existing behaviour of toggleOrderedList and toggleUnorderedList.

Motivation / 背景与动机

toggleOrderedList and toggleUnorderedList both support multi-line selections via the getLinesInRange + applyLines helpers in formatting.ts. However, toggleBlockquote was implemented as a single-line-only wrapper around the now-removed toggleLinePrefix helper, breaking consistency across the formatting API.

• Roadmap (docs/ROADMAP.md): Aligns with P1 toolbar completeness goal

Changes / 变更内容

• packages/plugin-toolbar:
  • src/formatting.ts: Rewrote toggleBlockquote to use getLinesInRange + applyLines, matching the list toggle pattern. In mixed-state mode, strips existing > before adding a new prefix (avoids > > text). Removed the now-unused toggleLinePrefix helper.
  • test/plugin-toolbar.test.ts: Added 16 test cases across 4 describe blocks — single-line backward compat, multi-line selection (6 cases including reversed/re-mixed/boundary), round-trip stability, and atomic undo (7 cases mirroring the existing list toggle test suite).

Testing / 测试

• pnpm test passes — 531 tests (515 existing + 16 new)
• pnpm typecheck passes — zero errors
• New vitest cases cover:
  • Single-line add/remove (backward compat guard)
  • Multi-line add/remove/mixed/reversed/boundary/end-of-doc
  • Round-trip stability (toggle on → off restores original)
  • Atomic undo Cases 1–7 (including the load-bearing Case 4 — proves single history entry)
• Manual UI check in electron-demo

Compliance / 合规自检

• CLA signed — first-time contributor
• AI disclosure: AI assistance used for test case generation and code review. Implementation logic designed and verified by human.
• New dependencies: none
• No build artifacts committed
• No secrets committed

Checklist / 自检清单

• Title follows Conventional Commits
• No public API changes
• Not touching live-preview-table.ts
• No breaking changes
• Change aligns with project scope (GOVERNANCE.md §4)

[CLAassistant]

All committers have signed the CLA.

[redreamality]

Reviewed PR #119.

This is a focused and well-scoped fix for toggleBlockquote multi-line behavior, aligning it with the existing ordered/unordered list toggle implementation style.

Validation performed in an isolated checkout:

pnpm exec tsc --noEmit -p packages/plugin-toolbar/tsconfig.json
pnpm --filter @floatboat/nexus-plugin-toolbar test -- plugin-toolbar --reporter=verbose
pnpm --filter @floatboat/nexus-plugin-toolbar test -- --runInBand
pnpm exec tsc --noEmit -p packages/core/tsconfig.json

These checks passed.

Review notes:

• CLA is passing.
• The implementation reuses the existing getLinesInRange / applyLines pattern used by list toggles instead of introducing a separate path.
• The PR preserves single-line behavior while adding multi-line support.
• Mixed selected lines are normalized instead of producing nested > > text prefixes.
• The change keeps the replacement as a single transaction via replaceRange, which is important for atomic undo behavior.
• Test coverage is strong for the size of the change: single-line compatibility, multi-line add/remove, mixed selections, reversed selection, line-boundary behavior, round-trip stability, and undo atomicity.

Conclusion: approved from code-review perspective.