Feature Request: Chart/Graph Footer Text Element

Summary Extend the existing chart title functionality to support an optional footer element positioned below the chart area. The footer would mirror the current title configuration experience -- dynamic text, font size control, and formatting options -- applied to a caption zone rendered beneath the visualization.

Use Case Chart titles are useful for labeling what a visualization shows, but there is currently no native way to add contextual footnotes or dynamic captions without workarounds. A footer element would allow report authors to:

• Add data source notes or methodology callouts directly beneath a chart
• Surface dynamic, measure-driven captions that explain what a user is seeing (e.g., "2026 reflects claims through March" or "National trend based on commercial population only")
• Include footnotes for suppressed values, benchmark definitions, or calculation caveats -- the kind of detail that belongs close to the chart but not in the title

Proposed Behavior The footer should behave identically to the title element in terms of configuration: optional display, free-text or dynamic expression input, font size and style control, and alignment options. Placement would be fixed below the chart plot area, above any axis labels or within the chart container padding. If the title and footer share the same configuration panel, a simple toggle or tab to switch between the two would keep the experience consistent.

Why This Matters As organizations use BI outputs for both internal analysis and external-facing reporting, the ability to annotate charts inline -- without layering separate text boxes and managing their positioning manually -- reduces report build time and improves consistency. This is particularly valuable in regulated or data-sensitive contexts like healthcare, where methodology transparency is expected.