feat: prompt to clear contexts when switching profiles

[aru-amedeo]

Problem

acloud config profile use switches credentials but leaves all saved contexts untouched.
Contexts store project IDs that belong to a specific tenant, so after switching to a different profile (e.g. from dev to prod) the saved project IDs are almost always invalid for the new tenant. The user then hits confusing 404 / permission errors on the first resource command.

Expected behaviour

When switching profiles, the CLI should offer to clear all saved contexts, because projects belong to a single tenant (profile). The user should be able to:

1. Accept the prompt to clear contexts in interactive mode
2. Pass --clear-contexts to clear without a prompt in scripts/CI
3. Decline the prompt (or run non-interactively) to keep contexts unchanged

Implemented behaviour

• Interactive: Contexts may not be valid for the new profile. Clear all contexts? (y/N):
• Non-interactive (piped): silently keeps contexts (safe default)
• --clear-contexts flag: always clears, no prompt

Fixed in #236.

[aru-amedeo]

closed by #236