feat(cli): V5 tier display names + error messages

[simple-agent-manager]

Summary

Updates all user-facing tier display names and pricing messages in the CLI to match V5 pricing.

Tier Display Name Changes

Proto Enum	Old Display	New Display
HOBBY (1)	Hobby	Starter
PERSONAL (2)	Personal	Starter (Legacy)
PRO (3)	Pro	Pro
TEAM (4)	Team	Enterprise
EXPIRED (-1)	Unknown	Expired
UNSPECIFIED (0)	(fell through to Hobby)	Starter

Other Changes

• GPU error: Now says "GPU access requires a Pro subscription ($49/mo). Upgrade at https://portal.defang.io/pricing"
• Estimate modes: Added tier requirement lines (Affordable: all tiers, Balanced: Pro $49/mo, HA: Enterprise $499/mo)
• Generate command: Short description mentions Starter limited generations/month, Pro unlimited
• Debug command: Short description mentions Pro requirement for full debugging
• whoami output: SubscriberTier field now shows human-readable V5 names instead of proto enum strings

Proto enums unchanged

Wire values (HOBBY=1, PERSONAL=2, PRO=3, TEAM=4) and proto enum names are NOT modified. This is display-only.

Test proof

$ go vet ./...     # passes (no output)
$ go build ./...   # passes (no output)
$ go test -short ./... | grep FAIL   # no failures

All existing tests pass including the updated golden output in estimate_test.go.

Test plan

• defang whoami shows "Starter" for hobby-tier accounts
• GPU deployment error shows new message with pricing URL
• defang estimate output includes tier requirement lines
• Verify backward compatibility with older Fabric versions (enum values unchanged)

🤖 Generated with Claude Code