feat: user-customizable draft welcome starters

Let users curate the draft welcome chips: pin existing commands and skills
as starters, remove them, and drag to reorder — all inline on the draft
screen via a '+' picker dialog and per-chip remove, with no separate
settings UI.

A starter references a command or skill; its scope is inherited from the
item (user-scope -> global, project-scope -> per-project). Global starters
persist to settings.json (useUIStore + client/server sanitizers); project
starters persist to the project config alongside worktree setup commands.
The two scopes form ordered namespaces shown global-first then project,
reorderable only within each group.

The six built-in Session magic-prompt commands are the default global set
and stay available in the picker for re-pinning if removed; they keep their
bespoke icons, while user commands/skills fall back to the Commands/Skills
section icons. Chip labels are normalized (/simplify-code -> 'Simplify
code'). Missing commands/skills are skipped rather than shown broken.

Drag-to-reorder works on desktop and mobile: rectSortingStrategy for the
wrapping multi-row layout, CSS.Translate (no scale) so the lifted chip
doesn't stretch, and MouseSensor + long-press TouchSensor so taps still
submit and swipes still scroll. The '+' picker is a searchable dialog on
every surface.

packages/web/server/lib/opencode/settings-helpers.js

@@ -145,6 +145,21 @@ export const createSettingsHelpers = (dependencies) => {
           .filter((entry) => typeof entry === 'string' && entry.length > 0)
       );
     }
+    if (Array.isArray(candidate.draftStarters)) {
+      const seenStarters = new Set();
+      const starters = [];
+      for (const entry of candidate.draftStarters) {
+        if (!entry || typeof entry !== 'object') continue;
+        const type = entry.type === 'command' || entry.type === 'skill' ? entry.type : null;
+        const name = typeof entry.name === 'string' ? entry.name.trim() : '';
+        if (!type || !name) continue;
+        const key = `${type}:${name}`;
+        if (seenStarters.has(key)) continue;
+        seenStarters.add(key);
+        starters.push({ type, name });
+      }
+      result.draftStarters = starters;
+    }
 
 
     if (typeof candidate.uiFont === 'string' && candidate.uiFont.length > 0) {