Implement export command

[asphaltbuffet]

This pull request introduces the new export command, enabling users to stream the full event log as NDJSON for backup or migration, and makes several documentation and codebase improvements. The most important changes are summarized below.

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New Feature: Export Command

• Adds a new export command to the CLI, which outputs all events as newline-delimited JSON (NDJSON), ordered by event_id ASC. Includes support for --quiet (suppresses "no events" warning) and a no-op --json flag for scripting consistency. The new command is fully tested. [1] [2] [3] [4] [5] [6] [7]

Documentation Updates

• Updates the README.md with usage instructions and reference to the new export command. [1] [2]
• Adds a changelog entry for version 0.4.0, detailing the export feature and related changes. [1] [2]
• Refines and expands internal documentation (.serena/memories/*.md) for conventions, core structure, tech stack, suggested commands, and task completion—clarifying command wiring, error handling, styles, and build/test practices. [1] [2] [3] [4] [5]

Codebase Maintenance

• Removes unused //go:generate mockery directives from command packages that no longer require generated mocks, cleaning up test scaffolding. [1] [2] [3] [4]

Configuration

• Updates .claude/settings.local.json to include permissions for the new export-related MCP server method.