feat(cursor): support modern agent transcript JSONL sessions

[lesbass]

What

Add support for modern Cursor Agent transcript JSONL files under ~/.cursor/projects/*/agent-transcripts/*/*.jsonl, while preserving the existing SQLite provider for legacy Cursor sessions.

Fixes #311.

Why

Recent Cursor versions write Agent conversations as per-session JSONL transcripts. The existing provider only searches Cursor's VS Code-style workspaceStorage and globalStorage SQLite databases, so these newer sessions are silently missed during sync.

The new transcript format contains user and assistant records shaped as { role, message: { content } }, plus lifecycle records such as turn_ended. Content may be a string or an array containing text, thinking, and tool-use blocks.

How

cli/src/providers/cursor.ts

• Discover main-session JSONL files under Cursor's modern agent-transcripts hierarchy.
• Parse string and block-array message content.
• Extract text, thinking, and tool-use inputs; skip lifecycle and malformed records safely.
• Strip Cursor's <user_query> wrapper from human prompts.
• Resolve project paths from worker.log when available, then fall back to best-effort decoding of Cursor's project slug.
• Apply the existing project filter to modern transcript directories.
• Keep session IDs compatible with existing Cursor records (cursor:<session-id>).
• Prefer the richer legacy SQLite representation when the same UUID exists in both sources.
• Support CURSOR_AGENT_HOME for copied/isolated Cursor data directories.

cli/src/providers/__tests__/cursor.test.ts

• Add synthetic fixtures for modern JSONL discovery and parsing.
• Cover string content, block-array content, thinking, tool calls, lifecycle records, malformed lines, and project filtering.

Documentation

• Document the modern JSONL source alongside legacy SQLite storage.

Format limitations

• Cursor's JSONL export may omit tool outputs, token usage, model metadata, and per-message timestamps.
• The parser uses file birth/mtime as the session timestamp fallback when record timestamps are absent.
• Subagent JSONL files are intentionally excluded from top-level session discovery.

Schema Impact

• SQLite schema changed: no
• Types changed: no
• Server API changed: no
• Backward compatible: yes

Testing

• pnpm --filter @code-insights/cli build passes.
• Full CLI suite passes: 582/582 tests across 28 test files.
• Verified on a real recent Cursor macOS installation: modern transcript sessions are discovered and sync successfully.
• Test fixtures are synthetic and contain no private transcript data.