feat: add /weigh approach-comparison command to draft welcome

Add /weigh as a draft chip and command for the moment before planning —
when you know what to build but not how. Its hidden prompt investigates
the code, then lays out 2-3 genuinely distinct approaches with trade-offs
(complexity, risk, blast radius, effort) and a clear recommendation,
without writing a plan or code.

Follows the established command pattern: visible + hidden magic prompts
wired into command autocomplete, the submit handler, draft preset chips,
and the Magic Prompts settings page, with i18n across all locales. Adds a
scales-3 icon to the sprite.

packages/ui/src/lib/i18n/messages/en.settings.ts

@@ -226,6 +226,7 @@ export const settingsDict = {
   'settings.magicPrompts.sidebar.item.sessionFeaturePlan': 'Feature Planning',
   'settings.magicPrompts.sidebar.item.sessionCatchUp': 'Catch Up',
   'settings.magicPrompts.sidebar.item.sessionDebug': 'Debugging',
+  'settings.magicPrompts.sidebar.item.sessionWeigh': 'Weigh Options',
   'settings.magicPrompts.sidebar.item.sessionFusion': 'Fusion',
   'settings.remoteInstances.sidebar.title': 'Remote Instances',
   'settings.remoteInstances.sidebar.total': 'Total {count}',
@@ -1695,6 +1696,8 @@ export const settingsDict = {
   'settings.magicPrompts.page.group.sessionCatchUp.description': 'Prompts used by the /catch-up slash command: visible user message + hidden instructions. Inspects git state and branches on it — reconstructs intent from an in-progress diff, checks an open PR\'s review state, or summarizes recent commits.',
   'settings.magicPrompts.page.group.sessionDebug.title': 'Debugging',
   'settings.magicPrompts.page.group.sessionDebug.description': 'Prompts used by the /debug slash command: visible user message + hidden instructions. Runs a guided root-cause investigation — captures the symptom, forms hypotheses, checks them against the code, and confirms the cause before proposing a fix.',
+  'settings.magicPrompts.page.group.sessionWeigh.title': 'Weigh Options',
+  'settings.magicPrompts.page.group.sessionWeigh.description': 'Prompts used by the /weigh slash command: visible user message + hidden instructions. Investigates the code, then lays out 2-3 distinct approaches with trade-offs and a recommendation — without writing a plan or code.',
   'settings.magicPrompts.page.group.sessionFusion.title': 'Fusion',
   'settings.magicPrompts.page.group.sessionFusion.description': 'Prompts used when combining multi-run outputs into one final answer: visible user message + hidden instructions before source results.',
   'settings.magicPrompts.page.actions.resetting': 'Resetting...',