Use the platform navigation instead of a hand-built sidebar

[pallaoro]

The app built its own sidebar, so opening it inside a dashboard that renders
its own navigation showed the user two of them. <AppNav> from
@clawnify/app is a single definition that serves both cases: it paints the
app's sidebar when the app stands alone, and hands the same list to the host
when it is embedded, which then draws the rows itself.

What changed

• src/client/components/sidebar.tsx is gone; app.tsx declares the nav as
  data and wraps the shell in flex min-h-screen flex-col md:flex-row.
• Dashboard is the home item, so it is not a row of its own: the app's name
  opens it. Channels sits under a Settings group.
• Queue and Drafts carry live counts. They read the stats the app already
  holds, which now load at boot with the rest, because each view's posts
  list is filtered to that view and cannot be counted for this.
• reportLocation follows the router, so the host can restore the screen on
  reload.
• styles.css brings the rail onto this app's tokens and back to the shell's
  own proportions.

The specificity guard

The package ships @media (max-width:767px){.cn-nav{width:100%;flex-direction:row}}
at specificity (0,1,0), and these overrides are written at aside.cn-nav
(0,1,1) so they beat its inline <style>. Specificity resolves before source
order, so an unguarded width: 275px would win at every width and leave a
275px column on a phone. Everything about the rail's geometry therefore sits
inside @media (min-width: 768px); only paint and type are global.

Verified

Measured in the browser at both ends of that breakpoint:

Viewport	aside.cn-nav	Page scrollWidth
1280x800	275px wide column, flex-direction: column, 1px right border	1280px, no sideways scroll
390x844	390px wide strip, 61px tall, flex-direction: row, bottom border	390px, no sideways scroll

Clicking a row routes and the active row follows on both. Counts render from
real state (Queue 4, Drafts 3 against a fixture). vite build succeeds;
tsc --noEmit reports the same four pre-existing D1Database / R2Bucket
errors in src/server as main does and nothing new.