refactor(theme): centralize status colors and overlay tints in CSS vars

Introduce semantic theme variables (e.g. --color-success, --color-danger,
--color-warning, --color-info) and a set of overlay/tint/shadow variables
(--app-hover-tint, --app-raise-tint, --app-soft-tint, --app-overlay-shadow,
--app-menu-shadow, --app-float-shadow, etc.) and use them throughout
app.css in place of many hard-coded color, background and shadow values.

This change:
- replaces literal color tokens used for badges, pills, buttons, menus,
  toasts, borders and file icons with the new semantic variables
- switches several box-shadow and overlay usages to the new shadow vars
- harmonizes light-theme surface, border and scrollbar values to explicit
  variables for easier maintenance

No structural or behavioral changes; this is purely a visual/theming
refactor to make future theme adjustments and dark/light parity simpler.

src/lib/components/CreateReviewDialog.svelte

@@ -178,5 +178,5 @@
 <style>
   .ai-draft-action{display:flex;align-items:center;gap:12px}.ai-draft-action small{color:var(--color-ink-muted);line-height:1.5}.ai-draft-action button{flex-shrink:0}
   .repository-field{min-width:0;display:grid;gap:9px}.field-heading{display:flex;align-items:center;justify-content:space-between;font-weight:600}.field-heading small{font-size:10px;font-weight:400;color:var(--color-ink-faint)}
-  dialog{margin:auto;width:min(640px,calc(100vw - 40px));max-height:calc(100vh - 48px);padding:0;border:1px solid var(--color-border-subtle);border-radius:14px;background:var(--app-dialog-bg);color:var(--color-ink);box-shadow:var(--app-dialog-shadow);font-family:inherit;font-size:12px;overflow:auto}dialog::backdrop{background:#0007;backdrop-filter:blur(3px)}header{display:flex;align-items:center;gap:12px;padding:22px 26px;background:var(--app-dialog-chrome);border-bottom:1px solid var(--color-border-subtle)}h2{margin:0;font-size:16px;font-weight:650}p{margin:5px 0 0;color:var(--color-ink-muted)}.heading-icon{display:grid;place-items:center;width:38px;height:38px;border-radius:10px;background:color-mix(in srgb,var(--color-accent) 12%,transparent);color:var(--color-accent)}button,input,textarea{font:inherit}button{display:inline-flex;justify-content:center;align-items:center;gap:8px;border:1px solid var(--color-border-subtle);border-radius:7px;padding:9px 13px;background:var(--color-surface);color:var(--color-ink);cursor:pointer}button:disabled{opacity:.5;cursor:default}.close{margin-left:auto;border:0;padding:6px}.body{display:grid;gap:20px;padding:24px 26px}label{display:grid;gap:8px;font-weight:600;min-width:0}input,textarea{box-sizing:border-box;width:100%;padding:10px 11px;border:1px solid var(--color-border-subtle);border-radius:7px;background:var(--app-bg);color:var(--color-ink);font-weight:400}input:focus,textarea:focus{outline:2px solid var(--color-accent);outline-offset:1px}textarea{resize:vertical;min-height:110px;line-height:1.6}.branches{padding:16px;background:color-mix(in srgb,var(--color-accent) 3%,var(--app-bg));border:1px solid var(--color-border-subtle);display:grid;grid-template-columns:minmax(0,1fr) 16px minmax(0,1fr);gap:12px;align-items:end}.branches>:global(svg){margin-bottom:12px;color:var(--color-accent)}.hint{margin-top:-8px;font-size:11px;line-height:1.5}.error,.validation{color:var(--color-danger,#e76767);line-height:1.5}.error{padding:12px;border-radius:7px;background:color-mix(in srgb,var(--color-danger,#e76767) 9%,transparent);overflow-wrap:anywhere}.error button{margin-left:8px}footer{display:flex;justify-content:flex-end;gap:9px;padding:16px 26px;background:var(--app-dialog-chrome);border-top:1px solid var(--color-border-subtle)}.primary{background:var(--color-accent);border-color:var(--color-accent);color:white}.primary:enabled:hover{filter:brightness(1.08)}:global(.spin){animation:rotate 1s linear infinite}@keyframes rotate{to{transform:rotate(360deg)}}
+  dialog{margin:auto;width:min(640px,calc(100vw - 40px));max-height:calc(100vh - 48px);padding:0;border:1px solid var(--color-border-subtle);border-radius:14px;background:var(--app-dialog-bg);color:var(--color-ink);box-shadow:var(--app-dialog-shadow);font-family:inherit;font-size:12px;overflow:auto}dialog::backdrop{background:color-mix(in srgb, var(--app-dialog-backdrop) 92%, transparent);backdrop-filter:blur(3px)}header{display:flex;align-items:center;gap:12px;padding:22px 26px;background:var(--app-dialog-chrome);border-bottom:1px solid var(--color-border-subtle)}h2{margin:0;font-size:16px;font-weight:650}p{margin:5px 0 0;color:var(--color-ink-muted)}.heading-icon{display:grid;place-items:center;width:38px;height:38px;border-radius:10px;background:color-mix(in srgb,var(--color-accent) 12%,transparent);color:var(--color-accent)}button,input,textarea{font:inherit}button{display:inline-flex;justify-content:center;align-items:center;gap:8px;border:1px solid var(--color-border-subtle);border-radius:7px;padding:9px 13px;background:var(--color-surface);color:var(--color-ink);cursor:pointer}button:disabled{opacity:.5;cursor:default}.close{margin-left:auto;border:0;padding:6px}.body{display:grid;gap:20px;padding:24px 26px}label{display:grid;gap:8px;font-weight:600;min-width:0}input,textarea{box-sizing:border-box;width:100%;padding:10px 11px;border:1px solid var(--color-border-subtle);border-radius:7px;background:var(--app-bg);color:var(--color-ink);font-weight:400}input:focus,textarea:focus{outline:2px solid var(--color-accent);outline-offset:1px}textarea{resize:vertical;min-height:110px;line-height:1.6}.branches{padding:16px;background:color-mix(in srgb,var(--color-accent) 3%,var(--app-bg));border:1px solid var(--color-border-subtle);display:grid;grid-template-columns:minmax(0,1fr) 16px minmax(0,1fr);gap:12px;align-items:end}.branches>:global(svg){margin-bottom:12px;color:var(--color-accent)}.hint{margin-top:-8px;font-size:11px;line-height:1.5}.error,.validation{color:var(--color-danger);line-height:1.5}.error{padding:12px;border-radius:7px;background:color-mix(in srgb,var(--color-danger) 9%,transparent);overflow-wrap:anywhere}.error button{margin-left:8px}footer{display:flex;justify-content:flex-end;gap:9px;padding:16px 26px;background:var(--app-dialog-chrome);border-top:1px solid var(--color-border-subtle)}.primary{background:var(--color-accent-solid);border-color:var(--color-accent-solid);color:var(--color-on-accent)}.primary:enabled:hover{filter:brightness(1.08)}:global(.spin){animation:rotate 1s linear infinite}@keyframes rotate{to{transform:rotate(360deg)}}
 </style>