refactor: replace cyan accent with ember orange across entire frontend

Swap accent color from cyan (#22d3ee) to ember orange (#f97316) site-wide.
Cyan caused contrast issues and felt generic — orange brings warmth and
urgency fitting for a troubleshooting tool.

Changes:
- CSS variables: accent, accent-hover, accent-dim, accent-text, primary, ring
- Warning color shifted from amber (#fbbf24) to yellow (#eab308) for
  semantic separation from orange accent
- Brand SVGs: logo gradient updated to orange
- 50+ component files: all hardcoded cyan hex values, Tailwind cyan-*
  classes, and rgba(34,211,238,...) glow values replaced
- landing.css: all 45+ cyan references + 5 old border color fixes
- DESIGN-SYSTEM.md bumped to v5 with decisions log
- CLAUDE.md: all color references synced to charcoal palette + orange accent
- PWA theme-color meta tag updated to match sidebar (#10121a)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/library/TreeGridView.tsx

@@ -145,7 +145,7 @@ export function TreeGridView({
                   onClick={() => onPrepareSession(tree)}
                   className={cn(
                     'rounded-md border border-border p-2 text-muted-foreground',
-                    'hover:bg-cyan-500/10 hover:text-cyan-400 hover:border-cyan-500/30'
+                    'hover:bg-orange-500/10 hover:text-orange-400 hover:border-orange-500/30'
                   )}
                   title="Prepare session for engineer"
                   aria-label="Prepare session"

frontend/src/components/library/TreeListView.tsx

@@ -148,7 +148,7 @@ export function TreeListView({
                   onClick={() => onPrepareSession(tree)}
                   className={cn(
                     'rounded-md border border-border p-1.5 text-muted-foreground',
-                    'hover:bg-cyan-500/10 hover:text-cyan-400 hover:border-cyan-500/30'
+                    'hover:bg-orange-500/10 hover:text-orange-400 hover:border-orange-500/30'
                   )}
                   title="Prepare session for engineer"
                   aria-label="Prepare session"

frontend/src/components/library/TreeTableView.tsx

@@ -252,7 +252,7 @@ export function TreeTableView({
                       onClick={() => onPrepareSession(tree)}
                       className={cn(
                         'rounded-md border border-border p-1.5 text-muted-foreground',
-                        'hover:bg-cyan-500/10 hover:text-cyan-400 hover:border-cyan-500/30'
+                        'hover:bg-orange-500/10 hover:text-orange-400 hover:border-orange-500/30'
                       )}
                       title="Prepare session for engineer"
                       aria-label="Prepare session"