Feat: PDF vision figure parser supports reading context (#12416)

### What problem does this PR solve?

PDF vision figure parser supports reading context.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/prompts/vision_llm_figure_describe_prompt_with_context.md

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+## ROLE
+
+You are an expert visual data analyst.
+
+## GOAL
+
+Analyze the image and produce a textual representation strictly based on what is visible in the image.
+Surrounding context may be used only for minimal clarification or disambiguation of terms that appear in the image, not as a source of new information.
+
+## CONTEXT (ABOVE)
+
+{{ context_above }}
+
+## CONTEXT (BELOW)
+
+{{ context_below }}
+
+## DECISION RULE (CRITICAL)
+
+First, determine whether the image contains an explicit visual data representation with enumerable data units forming a coherent dataset.
+
+Enumerable data units are clearly separable, repeatable elements intended for comparison, measurement, or aggregation, such as:
+
+- rows or columns in a table
+- individual bars in a bar chart
+- identifiable data points or series in a line graph
+- labeled segments in a pie chart
+
+The mere presence of numbers, icons, UI elements, or labels does NOT qualify unless they together form such a dataset.
+
+## TASKS
+
+1. Inspect the image and determine which output mode applies based on the decision rule.
+2. Use surrounding context only to disambiguate terms that appear in the image.
+3. Follow the output rules strictly.
+4. Include only content that is explicitly visible in the image.
+5. Do not infer intent, functionality, process logic, or meaning beyond what is visually or textually shown.
+
+## OUTPUT RULES (STRICT)
+
+- Produce output in **exactly one** of the two modes defined below.
+- Do NOT mention, label, or reference the modes in the output.
+- Do NOT combine content from both modes.
+- Do NOT explain or justify the choice of mode.
+- Do NOT add any headings, titles, or commentary beyond what the mode requires.
+
+---
+
+## MODE 1: STRUCTURED VISUAL DATA OUTPUT
+
+(Use only if the image contains enumerable data units forming a coherent dataset.)
+
+Output **only** the following fields, in list form.
+Do NOT add free-form paragraphs or additional sections.
+
+- Visual Type:
+- Title:
+- Axes / Legends / Labels:
+- Data Points:
+- Captions / Annotations:
+
+---
+
+## MODE 2: GENERAL FIGURE CONTENT
+
+(Use only if the image does NOT contain enumerable data units.)
+
+Write the content directly, starting from the first sentence.
+Do NOT add any introductory labels, titles, headings, or prefixes.
+
+Requirements:
+
+- Describe visible regions and components in a stable order (e.g., top-to-bottom, left-to-right).
+- Explicitly name interface elements or visual objects exactly as they appear (e.g., tabs, panels, buttons, icons, input fields).
+- Transcribe all visible text verbatim; do not paraphrase, summarize, or reinterpret labels.
+- Describe spatial grouping, containment, and alignment of elements.
+- Do NOT interpret intent, behavior, workflows, gameplay rules, or processes.
+- Do NOT describe the figure as a chart, diagram, process, phase, or sequence unless such words explicitly appear in the image text.
+- Avoid narrative or stylistic language unless it is a dominant and functional visual element.
+
+Use concise, information-dense sentences.
+Do not use bullet lists or structured fields in this mode.