Changes:
+ present not-found page for unhandled uri paths, eg /stuff
+ display the tip-height on front page
+ add favicon and neptune logo to front page
+ use ServerDir instead of ServeFile for /image and /css
+ add help tooltips for fields on front page
+ use monospace font for digests
Changes:
1. integrates pico minimal responsive css framework for light/dark
themes and overall better looks.
2. adds a not-found page for bad url queries.
3. catches axum/serde deserialization errors of user input and routes
them to the not-found page with a helpful hint (parse error msg)
