Improve generated graph HTML explorer

[DevStudio2k25]

Summary

• Redesigns the generated graph.html explorer with a compact canvas-style layout.
• Adds a tabbed sidebar for node info, hubs, and community controls.
• Adds confidence/evidence filters for EXTRACTED, INFERRED, and AMBIGUOUS edges.
• Improves large graph usability with an explore-first seed view, bounded expansion, cached node/edge lookups, and a bottom command/search bar.
• Adds dark/light theme support while preserving the existing embedded, no-server HTML export model.

Why

The previous HTML view loads every node and sidebar control into one dense panel, which becomes hard to scan on larger code graphs. This update keeps the same data contract and export path while making the output easier to navigate and less visually noisy.

Validation

• python -m py_compile graphify/export.py
• python -m pytest tests/test_export.py tests/test_pipeline.py -q

I also ran the full local suite after installing CI extras. It collected and ran, with unrelated local/environment failures from a stale installed skill version, the Windows case-collided sample.F90 fixture in my checkout, and local DNS resolution for arxiv.org.

Notes

This PR only changes graphify/export.py. No generated graphify-out artifacts are included.

[safishamsi]

The HTML explorer redesign looks great conceptually — the tabbed sidebar, command bar, and evidence filters are all useful additions.

However the diff has a UTF-8 encoding problem that blocks the merge. Your editor saved the file in latin-1, which corrupted every non-ASCII character in export.py — including em-dashes and arrows in functions like to_obsidian, safe_name, and to_svg that your PR doesn't intend to touch. Merging as-is would silently break unrelated exporters.

To fix: re-create the changes from a fresh checkout of v7, make sure your editor is set to UTF-8, and restrict the diff strictly to the HTML explorer sections (_html_styles, _html_script, to_html). The unrelated to_obsidian / to_svg context lines in the current diff show the corruption clearly.

Happy to merge once the encoding is clean — the feature itself is worth having.