feat: support {App, Path} tuples in static routes

[Taure]

Summary

• Support {App, Path} tuples in static routes to serve files from any dependency's priv directory
• Enables libraries like arizona_core to serve their own JS/CSS assets without copying files

Usage

routes(_Env) ->
    [#{prefix => "", routes => [
        %% Serve app's own static assets (existing behaviour)
        {"/assets/[...]", "static/assets"},
        %% Serve arizona_core's JS/CSS from its priv dir
        {"/arizona/[...]", {arizona_core, "static/assets"}}
    ]}].

Why

Currently Nova's static routes only resolve files from the current application's priv directory. This forces libraries to require users to copy assets into their app's priv. Phoenix/LiveView solves this by allowing deps to serve from their own priv — this brings the same capability to Nova.

The immediate use case is arizona_core serving arizona.min.js directly, but it works for any dependency that ships static assets.

Implementation

One new parse_url clause matching {RemotePath, {DepApp, LocalPath}}. Resolves via code:priv_dir(DepApp) and creates the appropriate nova_file_controller handler — same mechanism as existing string-based static routes.

Test plan

• All 347 existing tests pass
• Manual test with arizona_core serving JS via {arizona_core, "static/assets"}