fix(studio): sidebar — fix icon-shift + use collapsed top space

Two UX bugs Stefan flagged on the v0.51.0 collapsible rail:

1. Icons re-positioned when the rail expanded. Operators
   already pointing at an icon had to chase it as the rail
   grew. Two causes: the _SidebarItem switched between
   `Center(icon)` (collapsed) and `Row(icon, gap, label)`
   (expanded), and the AnimatedContainer's horizontal padding
   switched between FaiSpace.sm (collapsed) and FaiSpace.md
   (expanded). Both flipped the icon's effective X-position.

   Now: same Row, same AnimatedContainer padding, in both
   states. The icon sits at the same X-pixel always; only
   the label slot toggles open beside it.

2. Top of the collapsed rail was wasted (only the brand-mark
   was visible; version + connection + channel disappeared
   completely). Use the same vertical real estate for
   glance-able compact equivalents:

   * tiny "v0.51" version text in mono below the brand
   * _CollapsedConnectionDot — 10 px circle, green/red/amber
     tonality matching FaiDeltaMark's mode states. Tooltip
     surfaces the full endpoint string.
   * _CollapsedChannelChip — 18 px circle with the channel's
     first letter (P / B / D / L) in the same accent tone
     the full pill uses, so "production" stays unmistakably
     red even at-a-glance.

When the rail expands, the full pills replace the compact
indicators as before. Tests still green (the existing widget
test booted without hover-expand and that path stays correct
either way).

Version: 0.51.0 → 0.51.1
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

pubspec.yaml

@@ -1,7 +1,7 @@
 name: fai_studio
 description: "F∆I Studio — desktop GUI for the F∆I hub"
 publish_to: 'none'
-version: 0.51.0
+version: 0.51.1
 
 environment:
   sdk: ^3.11.0-200.1.beta