feat: add LaTeX/TikZ export for generated diagrams and plots (#137)

[itdeveloper1988]

feat: add LaTeX/TikZ export for generated diagrams and plots (#137)

Problem

Academic publishers (IEEE, ACL, NeurIPS) require editable .tex source
files for figures. The current raster-only output (PNG/JPEG/WebP)
forced researchers to manually redraw generated diagrams in TikZ after
using PaperBanana for the conceptual work.

Changes

paperbanana/agents/tikz_exporter.py (new)

TikZExporterAgent extending BaseAgent; VLM call at temperature=0.2
with image + context; strips markdown code fences via regex;
prepends metadata header with version, model, venue, diagram type

prompts/diagram/tikz_exporter.txt (new)

prompts/plot/tikz_exporter.txt (new)

Prompt templates for TikZ and PGFPlots output with escaped braces

paperbanana/core/config.py

export_tikz and export_pgfplots boolean settings with YAML key_map

paperbanana/core/types.py

TIKZ_EXPORTER_START/END progress stages; tikz_path field on
GenerationOutput

paperbanana/core/pipeline.py

Instantiates TikZExporterAgent in init with prompt_recorder;
runs export after final image save with progress events, cost
tracking, and graceful error handling; _get_version() helper

paperbanana/cli.py

--export-tikz on generate; --export-pgfplots on plot; standalone
tikz subcommand for post-hoc conversion of existing images

tests/test_tikz_exporter.py (new, 19 tests)

_extract_code fence stripping (8 cases including case-insensitive)
Agent run with mocked VLM (header content, diagram type routing)
Config/types field defaults and overrides
CLI input validation (missing file, invalid type, invalid venue)

Behavior after this change

$ paperbanana generate --input method.txt --caption "..." --export-tikz

Saves final_output.png and final_output.tex side by side.

$ paperbanana tikz --input outputs/run_abc/final_output.png

Converts an existing image to a .tex file in the same directory.

Closes #137

[itdeveloper1988]

@YB0y can you please review my PR and give me feedback?

Thanks.

[dippatel1994]

Hey @itdeveloper1988, heads up that PR #143 by @YB0y implements the same TikZ/LaTeX export for the same issue #137. This PR has better test coverage (19 tests) while #143 ships examples/tikz_export.py. Could you two coordinate on a single PR? Also lint is failing here - please run ruff check && ruff format and push.

[dippatel1994]

Hey @itdeveloper1988, after the recent updates PR #143 by @YB0y has become the more complete implementation (14 tests, PGFPlots support, venue/header metadata, post-hoc tikz CLI subcommand). I'm going to close this PR in favor of #143 to avoid duplication. Thank you for the contribution! Please feel free to follow up with additional improvements on top of #143 once it merges.