[codex] Unify chart standards and add B3 monthly index data

[robertoecf]

Summary

• Unifies the repository chart contract around the Chart Lab visual/informational structure while keeping renderer choice flexible.
• Adds B3 IndexStatisticsProxy monthly index evolution support for Ibovespa/B3 index charts via source wrapper, REST route, CLI command, docs, and mocked tests.
• Updates Chart Lab metadata/technical line, color mapping, primary-source naming, and adds an Ibovespa monthly preset.

Root cause / context

Agents had conflicting guidance between AGENTS.md, docs/CHART_STANDARDS.md, and the live Chart Lab implementation: old chart docs used different colors, incomplete mandatory metadata, and ambiguous renderer guidance. Also, simple Selic vs Ibovespa prompts lacked a repo-exposed B3 monthly index wrapper.

Validation

• .venv/bin/ruff format --check src/ tests/ scripts/
• .venv/bin/ruff check src/ tests/ scripts/
• .venv/bin/python -m mypy src/findata
• .venv/bin/python -m pytest tests/ -q (230 passed, 16 deselected)
• Live smoke: .venv/bin/findata b3 index-monthly IBOV --start 2026-01-01 --end 2026-05-11

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 703f498a-0cc6-4c1f-8b0f-1e76b2c9d7f8

📥 Commits

Reviewing files that changed from the base of the PR and between b244e50 and 5dcfdac.

📒 Files selected for processing (13)

• AGENTS.md
• README.md
• docs/CHART_STANDARDS.md
• docs/SOURCES_AND_ENDPOINTS.md
• src/findata/api/app.py
• src/findata/api/routers/b3.py
• src/findata/cli.py
• src/findata/sources/b3/__init__.py
• src/findata/sources/b3/indices.py
• src/findata/web/static/chart-explorer.js
• src/findata/web/templates/charts.html
• tests/test_api.py
• tests/test_b3_cotahist_indices.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/chart-contract-b3-monthly

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[gemini-code-assist]

Code Review

This pull request establishes a comprehensive standard for financial chart generation within the project, introducing the 'Chart Lab' as the canonical reference for visual and informational structure. It updates documentation to mandate a 'minimum information contract'—including extraction timestamps, audit data paths, and specific color tokens—to ensure all charts are reproducible and auditable. On the implementation side, a new API endpoint and CLI command have been added to fetch monthly closing levels for B3 indices (e.g., IBOV) using the IndexStatisticsProxy. The web-based chart explorer was also updated with new presets and enhanced technical metadata in the footer. Feedback was provided regarding a potential edge-case crash in the date calculation logic for historical windows.