Fix XLSX Indic script rendering in classic164

[shps951023]

Summary

The XLSX benchmark case classic164_indic_scripts still showed a visible mismatch: the MiniPdf output kept the Indic sample column blank while the reference rendered Devanagari, Tamil, Bengali, Telugu, and Gujarati text.

Root Cause

MiniPdf embedded Unicode fonts by mapping Unicode code points directly to CID glyphs, but Indic scripts require shaping. A code point to CID mapping is not enough for these scripts, so the visual output could be missing or incorrectly formed even when text extraction stayed correct.

Proposed Flow

1. Preserve extractable Unicode text in the PDF.
2. Render Indic XLSX cell text through the platform text shaper into transparent PNG overlays.
3. Commit the rendering fix with the refreshed benchmark artifacts.
4. Push the commit and trace the benchmark result.
5. Close this issue after the pushed fix is verified.

Validation Target

Run scripts/Run-Benchmark.ps1 -Filter "classic164" and confirm classic164_indic_scripts renders Indic glyphs in classic164_indic_scripts_p1_minipdf.png.

[shps951023]

Workflow update:

1. Reproduced the mismatch in classic164_indic_scripts: MiniPdf preserved text extraction but did not visibly render the Indic samples.
2. Identified the rendering gap as missing complex-script shaping for Indic text in the PDF text path.
3. Implemented an XLSX fallback that renders Indic cell text as transparent PNG overlays while keeping the original Unicode text hidden and extractable in the PDF.
4. Re-ran scripts/Run-Benchmark.ps1 -Filter "classic164"; the MiniPdf output now renders the Indic samples and the case score is 0.9979.
5. Next steps: commit, push, trace the pushed commit, then close this issue.

[shps951023]

Tracing update:

• Commit pushed to origin/main: 51e2655507115b8e9139e738c5cf5c0de8b919c1
• Commit message: Fix XLSX Indic script rendering (#87)
• Focused validation before push: scripts/Run-Benchmark.ps1 -Filter "classic164"
• Result: classic164_indic_scripts now renders Indic glyphs in the MiniPdf output; case score is 0.9979.
• Build validation before push: dotnet build src/MiniPdf/MiniPdf.csproj --no-restore
• GitHub commit status API returned pending with no status contexts, so there are no remote checks to wait for on this commit.

Closing this issue as fixed by 51e2655507115b8e9139e738c5cf5c0de8b919c1.

[shps951023]

Closed after tracing pushed commit 51e2655 and confirming the focused classic164 benchmark output.