Polish UI: SearchBar sizing, SessionList layout, Tooltip offset, and progress CSS

SearchBar:
- Switch from fixed w-80/sm:w-96 to fluid min-w-80 max-w-md w-full
- Adjust left padding for better visual alignment with search icon

SessionList:
- Memoize project grouping computation with useMemo
- Move horizontal padding from per-item margin (mx-2 + width calc hack)
  to container padding (px-2) for cleaner layout and full-width buttons
- Remove inline width override that was compensating for the old margins

Tooltip:
- Increase offset from 8px to 12px for better visual separation

CSS:
- Add prose-message-progress variant with compact 11px mono typography
  for progress event content (code blocks, tables, links, blockquotes)
- Reduce search minimap marker height from 4px to 3px
- Normalize prose-message line-height: paragraphs 1.625→1.6, list
  items 1.5→1.6 for consistent rhythm
- Switch custom checkbox checkmark sizing from fixed px to percentages
  for better scaling across different zoom levels

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/client/styles/main.css

@@ -247,7 +247,7 @@ mark.search-highlight {
   position: absolute;
   right: 0;
   width: 8px;
-  height: 4px;
+  height: 3px;
   background: rgba(254, 240, 138, 0.7);
   border: none;
   padding: 0;
@@ -362,7 +362,7 @@ mark.search-highlight {
 .prose-message p {
   margin-top: 0.5rem;
   margin-bottom: 0.5rem;
-  line-height: 1.625;
+  line-height: 1.6;
 }
 
 .prose-message p:first-child {
@@ -383,7 +383,7 @@ mark.search-highlight {
 .prose-message li {
   margin-top: 0.25rem;
   margin-bottom: 0.25rem;
-  line-height: 1.5;
+  line-height: 1.6;
 }
 
 .prose-message code:not(pre code) {
@@ -445,6 +445,116 @@ mark.search-highlight {
   font-weight: 600;
 }
 
+/* ═══════════════════════════════════════════════
+   Progress markdown (compact variant)
+   ═══════════════════════════════════════════════ */
+
+.prose-message-progress {
+  font-family: "JetBrains Mono", "Fira Code", "SF Mono", ui-monospace, monospace;
+  font-size: 11px;
+  line-height: 1.5;
+  color: var(--color-foreground-secondary);
+  word-break: break-word;
+}
+
+.prose-message-progress h1,
+.prose-message-progress h2,
+.prose-message-progress h3,
+.prose-message-progress h4,
+.prose-message-progress h5,
+.prose-message-progress h6 {
+  font-size: 12px;
+  font-weight: 600;
+  color: var(--color-foreground);
+  margin-top: 0.25rem;
+  margin-bottom: 0.25rem;
+}
+
+.prose-message-progress p {
+  margin-top: 0.125rem;
+  margin-bottom: 0.125rem;
+}
+
+.prose-message-progress p:first-child {
+  margin-top: 0;
+}
+
+.prose-message-progress p:last-child {
+  margin-bottom: 0;
+}
+
+.prose-message-progress ul,
+.prose-message-progress ol {
+  margin-top: 0.25rem;
+  margin-bottom: 0.25rem;
+  padding-left: 1rem;
+}
+
+.prose-message-progress li {
+  margin-top: 0.125rem;
+  margin-bottom: 0.125rem;
+  line-height: 1.5;
+}
+
+.prose-message-progress code:not(pre code) {
+  font-family: inherit;
+  font-size: 0.9em;
+  padding: 0.0625rem 0.25rem;
+  border-radius: 0.1875rem;
+  background: var(--color-surface-inset);
+  border: 1px solid var(--color-border-muted);
+  color: #c4a1ff;
+  font-weight: 500;
+}
+
+.prose-message-progress pre {
+  margin-top: 0.5rem;
+  margin-bottom: 0.5rem;
+  max-width: 100%;
+  overflow-x: auto;
+}
+
+.prose-message-progress blockquote {
+  border-left: 2px solid var(--color-border);
+  padding-left: 0.5rem;
+  color: var(--color-foreground-secondary);
+  margin-top: 0.25rem;
+  margin-bottom: 0.25rem;
+}
+
+.prose-message-progress a {
+  color: var(--color-accent);
+  text-decoration: underline;
+  text-underline-offset: 2px;
+  text-decoration-color: rgba(91, 156, 245, 0.3);
+  transition: text-decoration-color 150ms;
+}
+
+.prose-message-progress a:hover {
+  color: var(--color-accent-dark);
+  text-decoration-color: rgba(125, 180, 255, 0.6);
+}
+
+.prose-message-progress table {
+  width: 100%;
+  border-collapse: collapse;
+  margin-top: 0.375rem;
+  margin-bottom: 0.375rem;
+  font-size: 11px;
+}
+
+.prose-message-progress th,
+.prose-message-progress td {
+  border: 1px solid var(--color-border-muted);
+  padding: 0.25rem 0.5rem;
+  text-align: left;
+}
+
+.prose-message-progress th {
+  background: var(--color-surface-inset);
+  font-weight: 600;
+}
+
 /* ═══════════════════════════════════════════════
    Focus ring system
    ═══════════════════════════════════════════════ */
@@ -481,10 +591,10 @@ mark.search-highlight {
 .custom-checkbox:checked::after {
   content: "";
   position: absolute;
-  top: 1px;
-  left: 4px;
-  width: 5px;
-  height: 9px;
+  top: 6.25%;
+  left: 25%;
+  width: 31.25%;
+  height: 56.25%;
   border: solid #0c1017;
   border-width: 0 2px 2px 0;
   transform: rotate(45deg);