fix: Stop mutating server-side org on org selection

[charlesvien]

Related issue to come back to this later #1101

1. Remove switchOrganization which PATCHed /@me to mutate the user's active org server-side
2. Simplify OrgBillingStep to just store the selection client-side (no async, no server mutation)
3. Add useAllOrgProjects hook (onboarding only) that fetches project details per-ID via project-scoped endpoints
4. Keep useProjects using currentUser.organization.teams (zero extra API calls on normal app load)

[charlesvien]

• fix: Stop mutating server-side org on org selection #1100 👈 (View in Graphite)
• fix: Update title prompt, scope reauth during onboarding, header overflow #1098 : 1 other dependent PR (#1091 )
• feat: Improve agent session lifeycle and bump SDKs #1089
• fix: Address feedback nits and bug reports (see desc) #1092
• main

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