Implement `optimize` — opinionated cost-saving recommendations

[glennmichael123]

Implementation issue split out from #107.

Replace the mock-data body in packages/ts-cloud/bin/commands/cost.ts (optimize command) with real implementation. Composes resources + resources:unused + cost:breakdown into actionable recommendations:

• Reserved Instance candidates (steady-state EC2 / RDS workloads).
• Right-sizing (EC2 / RDS instances < 20% utilization).
• Storage class transitions (S3 Standard → Intelligent-Tiering / Glacier).
• Unused resources (delete recommendation, sourced from `resources:unused`).
• CloudFront compression / caching wins (data transfer cost).

Acceptance

• cloud optimize returns real recommendations from the connected account.
• Each recommendation lists current cost, projected cost, savings, and the source signal (which CloudWatch metric / Cost Explorer line item triggered it).
• --profile honored.
• Replaces the cli.warn('not implemented') guard introduced by Stub commands in cost.ts return mock data — implement or guard with 'not implemented' warning #107.

Notes

• This is the heaviest of the five — depends on resources and resources:unused being real first. Last to implement.
• Some recommendations (RI commitments, Compute Savings Plans) need account-level commitment-tracking data; can stub those with a flag (--include-commitments) once the rest is real.

Related

• #107 — tactical guard