feat(oauth): add trips:share scope and redesign consent screen

Introduce trips:share as a dedicated OAuth scope for managing public
share links, decoupled from trips:read and trips:write. Share link
tools (get/create/delete_share_link) now gate on canShareTrips()
instead of the generic read/write scopes. Scope added to both client
and server definitions with full test coverage.

Redesign the consent screen from a narrow single-column card
(max-w-sm) to a two-panel layout (max-w-2xl): app identity and
action buttons on the left, scrollable scope list on the right.
Responsive — stacks vertically on mobile.

client/src/api/oauthScopes.ts

@@ -8,9 +8,10 @@ export interface ScopeInfo {
 }
 
 export const SCOPE_GROUPS: Record<string, ScopeInfo> = {
-  'trips:read':          { label: 'View trips & itineraries',   description: 'Read trips, days, day notes, members, and share links',                    group: 'Trips' },
+  'trips:read':          { label: 'View trips & itineraries',   description: 'Read trips, days, day notes, and members',                              group: 'Trips' },
   'trips:write':         { label: 'Edit trips & itineraries',   description: 'Create and update trips, days, notes, and manage members',                  group: 'Trips' },
   'trips:delete':        { label: 'Delete trips',               description: 'Permanently delete entire trips — this action is irreversible',              group: 'Trips' },
+  'trips:share':         { label: 'Manage share links',         description: 'Create, update, and revoke public share links for trips',                   group: 'Trips' },
   'places:read':         { label: 'View places & map data',     description: 'Read places, day assignments, tags, categories, and visited countries',      group: 'Places' },
   'places:write':        { label: 'Manage places',              description: 'Create, update, and delete places, assignments, tags, and atlas entries',    group: 'Places' },
   'packing:read':        { label: 'View packing lists',         description: 'Read packing items, bags, and category assignees',                          group: 'Packing' },