chore: bump version to 0.4.2

[chenyme]

✨ Feature

• Message deletion: Delete individual user or assistant messages while preserving subsequent messages and reconnecting the conversation; the first message and messages being generated are protected.
• OpenRouter image support: Added text-to-image generation and reference-image editing, with image model discovery and streaming responses where supported.
• Tiered pricing import: Import OpenRouter pricing tiers, including input, output, cache-read, and cache-write rates.
• Signed MCP user context: MCP calls can optionally carry signed user, conversation, and request information, enabling services to verify caller context.
• MCP header presets: Added quick-fill request headers, JSON validation, and protection against overwriting conflicting values.
• Embedding compatibility: Added an option to omit the dimensions parameter for embedding providers that do not accept it.

⚡ Optimization

• Dark theme: Adjusted background, border, and foreground contrast for clearer visual hierarchy.
• Per-device appearance: Light, dark, and system modes are now saved independently on each device instead of being overwritten by account synchronization.
• Chat navigation: Improved message-position and response-outline navigation, including heading alignment, active-section tracking, and hover targets.
• Markdown tables: Refined column widths, long-text wrapping, line spacing, and explicit line-break spacing.
• Admin scrolling: Pages can now scroll when the pointer is over the sidebar or page margins.
• Pricing configuration: Added clearer price units, tier ranges, and import warnings; tier limits now use full token counts instead of thousands.
• Upstream model status: Clearly marks models that have disappeared from upstream catalogs and explains route availability and automatic recovery.
• File indexing: Added a distinct “No text” state and count, plus an option to include these files when manually rebuilding indexes.

🐛 Fixed

• Fixed tool-call steps disappearing during long reasoning streams and improved preservation of reasoning content across rounds.
• Fixed rendering problems caused by nested code fences.
• Fixed excessive escaping when pasting rich content as Markdown.
• Fixed model submenus shifting unexpectedly on hover or close.
• Fixed table content bleeding above sticky headers.
• Fixed light-theme flashes when loading a page with dark mode selected.
• Fixed locked accounts being reported as invalid credentials; login errors now show the remaining lock duration.
• Fixed compatibility with upstreams that only accept a single leading system message, while preserving explicit prompt-cache behavior.
• Fixed repeated extraction and reindexing of files with no readable text.
• Fixed imported cache-write pricing calculations and aligned displayed prices with billing.
• Fixed raw JSON error output during upstream model synchronization.
• Improved error handling when deleting messages or replying to a message that has already been deleted.