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/ui/src/lib/draftStarters.ts

@@ -0,0 +1,83 @@
+import type { IconName } from "@/components/icon/icons";
+import type { I18nKey } from "@/lib/i18n";
+
+// A draft starter is a reference to an existing command or skill, pinned to the
+// onboarding/draft welcome screen as a one-click chip. Scope (global vs project)
+// is NOT stored here — it is encoded by which list the ref lives in (global =
+// settings.json, project = project config), derived from the command/skill's own
+// scope when pinned.
+export type DraftStarterType = 'command' | 'skill';
+
+export type DraftStarterRef = {
+    type: DraftStarterType;
+    name: string;
+};
+
+// Our built-in openchamber commands (Session magic prompts). They are always
+// available to pin, keep their bespoke icons, and seed the default global set.
+export type BuiltInStarter = {
+    name: string;
+    icon: IconName;
+    labelKey: I18nKey;
+    command: string;
+};
+
+export const BUILTIN_STARTERS: readonly BuiltInStarter[] = [
+    { name: 'explore', icon: 'compass-3', labelKey: 'chat.draftPresets.explore.label', command: '/explore' },
+    { name: 'catch-up', icon: 'history', labelKey: 'chat.draftPresets.catchup.label', command: '/catch-up' },
+    { name: 'weigh', icon: 'scales-3', labelKey: 'chat.draftPresets.weigh.label', command: '/weigh' },
+    { name: 'plan-feature', icon: 'survey', labelKey: 'chat.draftPresets.plan.label', command: '/plan-feature' },
+    { name: 'debug', icon: 'bug', labelKey: 'chat.draftPresets.debug.label', command: '/debug' },
+    { name: 'review', icon: 'search-eye', labelKey: 'chat.draftPresets.review.label', command: '/workspace-review' },
+];
+
+const BUILTIN_BY_NAME = new Map<string, BuiltInStarter>(BUILTIN_STARTERS.map((s) => [s.name, s]));
+
+export const getBuiltInStarter = (name: string): BuiltInStarter | undefined => BUILTIN_BY_NAME.get(name);
+export const isBuiltInStarter = (ref: DraftStarterRef): boolean =>
+    ref.type === 'command' && BUILTIN_BY_NAME.has(ref.name);
+
+// Default global starter set (used until the user customizes the global list).
+export const DEFAULT_GLOBAL_STARTERS: readonly DraftStarterRef[] = BUILTIN_STARTERS.map((s) => ({
+    type: 'command' as const,
+    name: s.name,
+}));
+
+// Fallback icons for user-defined starters, matching the Settings sections.
+export const COMMAND_FALLBACK_ICON: IconName = 'terminal-box';
+export const SKILL_FALLBACK_ICON: IconName = 'book-open';
+
+export const starterKey = (ref: DraftStarterRef): string => `${ref.type}:${ref.name}`;
+
+export const sameStarter = (a: DraftStarterRef, b: DraftStarterRef): boolean =>
+    a.type === b.type && a.name === b.name;
+
+// Turn a command/skill name into a human chip label: "/simplify-code" -> "Simplify code".
+export const normalizeStarterLabel = (name: string): string => {
+    const base = name
+        .replace(/^\//, '')
+        .replace(/[-_]+/g, ' ')
+        .replace(/\s+/g, ' ')
+        .trim();
+    if (!base) return name;
+    return base.charAt(0).toUpperCase() + base.slice(1);
+};
+
+// Parse persisted starter refs (from settings.json or project config) defensively.
+export const sanitizeStarterRefs = (value: unknown): DraftStarterRef[] => {
+    if (!Array.isArray(value)) return [];
+    const out: DraftStarterRef[] = [];
+    const seen = new Set<string>();
+    for (const entry of value) {
+        if (!entry || typeof entry !== 'object') continue;
+        const record = entry as Record<string, unknown>;
+        const type = record.type === 'command' || record.type === 'skill' ? record.type : null;
+        const name = typeof record.name === 'string' ? record.name.trim() : '';
+        if (!type || !name) continue;
+        const key = `${type}:${name}`;
+        if (seen.has(key)) continue;
+        seen.add(key);
+        out.push({ type, name });
+    }
+    return out;
+};