Custom agent controls and keyboard navigation

Custom agents can now switch off the default prompts and tools, and the agent you pick sticks with you after a reload. This release also adds Page Up, Page Down, Home, End, and Escape for moving around a conversation, speeds up switching conversations in the sidebar, and fixes a batch of settings and conversation state issues.

• Custom agents can now switch off the default prompt sections and default tools and add back only the tools they need.
• Page Up, Page Down, Home, and End now scroll through a conversation, and Escape steps out of the prompt box.
• The custom agent you pick in the message box is remembered after a reload, and resets to the main agent if that agent is deleted or turned off.
• Dragging a file over the chat now highlights the message box itself, so it is clearer where the file will land.
• The project picker above the message box now reads "No Project" when you are working outside of a project, instead of "New Conversation".
• Improved performance when switching between conversations in the sidebar.
• Bold text in chat now renders at a slightly lighter weight so it sits better with the text around it.
• Fixed an issue where your saved settings and project list could be overwritten when the app failed to read its state file.
• Fixed an issue where permission settings accumulated duplicate entries, which made conversation files grow very large and slowed the app down.
• Fixed an issue where starting a new conversation could show a false crash recovery notice.
• Fixed an issue where a conversation started without a folder pulled in files and settings from unrelated projects you had open.
• A command that is killed when the app restarts is now reported as canceled instead of appearing to finish successfully.
• The agent now reports a clear error when it tries to read a binary file it cannot display, instead of returning unreadable content.
• A malformed tool call from the model now appears as a short "Invalid tool call" note rather than a failure.
• Fixed an issue where an error that arrived without any tool activity in the turn was dropped instead of shown in the conversation.
• Fixed an issue where a system message could appear twice, or out of order, in the chat transcript.
• Fixed an issue where a turn ending in an error or a scheduled task showed an empty expandable section.
• Chat messages now fade out smoothly at the bottom of the conversation instead of being cut off sharply.
• The close-window shortcut now closes the dialog on top, such as settings, instead of the conversation behind it, and Escape inside an open menu now closes just the menu rather than the whole dialog.
• Fixed an issue where the projects list in settings could not be collapsed again after you expanded it.
• Fixed an issue where the side pane's tabs ran underneath the controls in the top-left corner of the window when the pane was maximized and the sidebar was collapsed.
• Fixed an issue where selected rows in the file tree and file path menus rendered with a heavy blue fill.
• Fixed an issue where sending feedback with large diagnostic logs attached failed, and removed an empty gap in the feedback form.