feat(theme): replace purple accent with teal/turquoise color scheme

Swaps violet (#8b5cf6) for teal (#14b8a6/#0d9488) across all components
and updates dark backgrounds to have a green-tinted hue instead of blue-navy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/index.css

@@ -16,11 +16,11 @@ input, textarea, button, select {
 
 /* ── Design system (dark only — no light mode in v1) ─────────────────────── */
 :root {
-  /* v2 dark-space palette */
-  --bg:          #0c0e1a;
-  --bg-card:     #10131f;
-  --bg-raised:   #151828;
-  --bg-hover:    #1a1e30;
+  /* v2 dark-teal palette */
+  --bg:          #080f0d;
+  --bg-card:     #0c1612;
+  --bg-raised:   #101c18;
+  --bg-hover:    #142420;
   --bg-subtle:   rgba(255,255,255,0.025);
   --bg-inset:    rgba(255,255,255,0.04);
   --border:      rgba(255,255,255,0.06);
@@ -29,12 +29,12 @@ input, textarea, button, select {
   --text:        #e8e9f0;
   --text-muted:  rgba(232,233,240,0.55);
   --text-subtle: rgba(232,233,240,0.28);
-  /* Violet accent */
-  --accent:      #8b5cf6;
-  --accent-light: #a78bfa;
-  --accent-hover: #9f70f8;
-  --accent-bg:   rgba(139,92,246,0.12);
-  --accent-border: rgba(139,92,246,0.3);
+  /* Teal accent */
+  --accent:      #14b8a6;
+  --accent-light: #2dd4bf;
+  --accent-hover: #10a89a;
+  --accent-bg:   rgba(20,184,166,0.12);
+  --accent-border: rgba(20,184,166,0.3);
   --accent-fg:   #ffffff;
   --teal:        #34d399;
   --teal-bg:     rgba(52,211,153,0.1);
@@ -53,7 +53,7 @@ input, textarea, button, select {
 /* Bottom Navigation Bar */
 nav[style*="position: fixed"] {
   display: flex;
-  background: #0b0b0e;
+  background: #060d0b;
   border-top: 1px solid rgba(255, 255, 255, 0.06);
   padding: 8px 16px;
 }