P10-T140: Write documentation for dashboard setup and local development

[garnizeh]

This pull request finalizes the documentation and developer guidance for the dashboard and monitoring UI (Phase 10). It adds comprehensive instructions for configuring, running, and developing the dashboard, including environment variables, usage, architecture, and troubleshooting. Additionally, it updates the status of related project tasks to reflect the completion or deferral of specific features.

Dashboard Documentation and Developer Guide:

• Added a new docs/api/ui-development.md file detailing the dashboard's tech stack, directory structure, HTMX/WebSocket usage, and step-by-step instructions for adding new statistics or components, as well as troubleshooting common issues.

README Enhancements:

• Documented the DASHBOARD_PASSWORD environment variable, including its purpose and effect on dashboard security.
• Expanded the README with a new section describing dashboard access, security, real-time updates, and links to the new developer guide.

Project Task Status Updates:

• Marked the dashboard documentation task (P10-T140) as completed, with all acceptance criteria checked off. [1] [2]
• Deferred the "Error Log and alert notifications" (P10-T120) and "Export functionality" (P10-T130) tasks, including reasons and future revisit notes. [1] [2]