quickshell: vertical left bar, 2x rounding, left-aligned surfaces

Bar moves from a horizontal top band to a vertical left column
(Theme.barHeight -> barWidth, 46px for the stacked HH/mm clock).
Every panel now grows rightward out of the bar instead of down:
the dropdown chrome's morph axis, the SDF surface geometry and the
session menu all swap x/y. The launcher is the one surface left at
bottom-centre, as asked.

New: NixOS snowflake at the top (recoloured to the accent with the
tray's hidden-Image + ColorOverlay trick), vertical workspace dots
whose focused pill grows on height, an inline OSD slot in the gap
between the two clusters, and a power button in the bottom-left
that opens the session menu.

Dropped the flush-to-far-edge dropdown special case — clamped
tracking plus the SDF melt already covers it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

settings/hyprland.nix

@@ -104,8 +104,8 @@ in
               # 6px of the outer gap is occupied by the quickshell screen
               # frame (Theme.frameWidth) — 18 on framed sides keeps the
               # visible frame↔window gap equal to the inter-window gap (12).
-              # Top stays 12: the bar reserves its own space.
-              gaps_out = { top = 12; right = 18; bottom = 18; left = 18; };
+              # Left stays 12: the bar lives there and reserves its own space.
+              gaps_out = { top = 18; right = 18; bottom = 18; left = 12; };
               border_size = 2;
               layout = "dwindle";
               resize_on_border = true;