How could one serve maps (tiles in wherever format possible) within a Android device to be consumed by an offline webmapping app also accessed within the device's browser?
There are a few options using TileMill/Mapbox/MBTiles... Not html5 though. You may want to explore other options for android than html5!!
MBTilesDroidSplitter : https://github.com/djcoin/MBTilesDroidSpitter
Locus : http://www.locusmap.eu/
Your webmapping offline code will be located in Assets folder.
You can put your tiles (XYZ or TMS) in a folder hierarchy inside Assets, too, and access your tiles via relative paths.
You really don't need a web server, the same way you don't need it to import a JS file into your HTML page.