feat(scale): implement scale up with real fleet provisioning simulation

[wjgong001]

Description

Replaces the scale up stub with a working fleet-provisioning simulation. Reads/writes ~/.sh1pt/credentials.json (same convention as PR #225 scale cost).

What it does

• sh1pt scale up --instances 3 --provider digitalocean — provisions N instances
• Reads current fleet from ~/.sh1pt/credentials.json (existing file convention)
• Selects provider automatically from existing fleet, or defaults to digitalocean
• Shows a plan preview with hourly costs before provisioning
• --max-hourly-price <usd> guardrail — rejects if new total exceeds ceiling
• --dry-run — shows the plan without modifying state
• Auto-assigns simulated IPs and updates the fleet file
• Multi-provider pricing table (11 providers from PR feat(scale): implement scale cost with real provider pricing data #225)

Guardrails

• Rejects --instances < 1
• Rejects unknown providers
• --max-hourly-price prevents cost overruns
• Inline spot instance savings hint when applicable

Type safety

Zero tsc --noEmit errors (same strict settings as rest of the repo).

Related

Closes the comment on uGig gig — delivering scale up as next deliverable under the $1 SOL/PR model.