Add generated graph visualizations and timelines

[kmosoti]

Summary

• Add created and updated frontmatter dates to graph source nodes and export them through nodes, chunks, concepts, and timeline artifacts.
• Generate README-linked SVG visualizations for the repo system, research support map, and knowledge base growth timeline.
• Generate timeline artifacts: graph/generated/timeline.jsonl, graph/generated/reports/timeline.md, and per-major-concept SVG timelines.
• Add tea-kb viz all plus focused timeline, system, and research visualization commands.
• Document the date/timeline/visualization standards and add a regression assertion for timeline export.

Validation

• uv run ruff check
• uv run ruff format --check
• uv run pyright
• uv run pytest
• uv run tea-kb validate
• uv run tea-kb build --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Prune concept timeline SVGs that fall out of the top set

When concept counts change so a previously generated major concept is no longer returned by major_concepts(graph), this dynamic artifact list stops including its concept-timeline-*.svg, but normal tea-kb build only writes the current artifacts and CI's .github/workflows/ci.yml runs tea-kb build --check, whose writer check only compares expected artifacts. That lets obsolete generated SVGs remain committed and still pass the build check; either generate a stable set or delete/check stale concept-timeline-*.svg files that are no longer expected.

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