feat: dark theme foundation — config.toml, Plotly template, CSS

[jschloman]

Summary

Establish the visual design system used by all subsequent visualization issues. This is a prerequisite for all other UI work.

See mockup: assets/dashboard_mockup.png

Palette — Deep Space Indigo

Role	Hex
App background	#0c1120
Card background	#141c2f
Sidebar background	#090e1a
Lifted / hover	#1e293b
Border	#2d3a52
Primary text	#f0f4ff
Secondary text	#8895a7
Muted text	#4b5a72
Primary accent (indigo)	#6366f1
Chart 2 (cyan)	#22d3ee
Chart 3 (pink)	#f472b6
Chart 4 (purple)	#a855f7
Chart 5 (green)	#22c55e
Chart 6 (orange)	#f97316
Chart 7 (yellow)	#facc15

Deliverables

1. .streamlit/config.toml

[theme]
base = "dark"
primaryColor = "#6366f1"
backgroundColor = "#0c1120"
secondaryBackgroundColor = "#141c2f"
textColor = "#f0f4ff"
borderColor = "#2d3a52"
font = "Inter:https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap"
chartCategoricalColors = ["#6366f1","#22d3ee","#f472b6","#a855f7","#22c55e","#f97316","#facc15"]

2. core/theme.py — global Plotly template

Define an autobio_dark Plotly template and set it as pio.templates.default. Import this module once at the top of visualize.py so all px.* charts inherit it automatically. Template must set paper_bgcolor, plot_bgcolor, font, colorway, axis grid colors, hover label styling, and legend styling.

3. CSS injection in visualize.py

Inject via st.markdown(..., unsafe_allow_html=True):

• Hide Streamlit's default header/footer chrome
• .block-container { padding-top: 1.5rem } for tighter layout
• Card border-radius and box-shadow defaults

4. requirements.txt

Add streamlit-extras for style_metric_cards().

Acceptance criteria

• streamlit run visualize.py loads with dark background, Inter font, indigo accent
• All existing px.* charts automatically use the dark template without per-chart changes
• ruff check ., mypy, and pytest all pass
• No hardcoded personal data introduced