feat(cli): agentcore sync gateway-targets command (SynchronizeGatewayTargets API)

[aidandaly24]

Description

The AgentCore control-plane API exposes a SynchronizeGatewayTargets action (referenced as the IAM permission required when enabling semantic search at gateway create time — see gateway-create devguide). This action forces a refresh of the gateway's tool catalog from all configured targets.

There is no corresponding CFN resource or property — CFN models desired-state, not synchronize actions. The CLI also has no surface for it: customers cannot trigger a re-sync after editing target tool definitions or after an upstream OpenAPI/Smithy schema changes.

Acceptance Criteria

• Add a new top-level CLI command: agentcore sync gateway-targets [--gateway <name>] [--target <name>].
• Implementation calls the control-plane SynchronizeGatewayTargets API for the specified gateway/target.
• If --gateway is omitted, sync all gateways in the project.
• If --target is omitted, sync all targets on the gateway(s).
• Surface a "Sync targets" action in the TUI gateway detail screen.
• Optional: hook a sync into agentcore deploy post-step when target tool definitions change (gated behind a --sync-after-deploy flag).
• Document the IAM permission required (bedrock-agentcore:SynchronizeGatewayTargets).

Acceptance Criteria — non-goals

• Not in scope: making sync run automatically on every deploy (user opt-in only).
• Not in scope: progress / status streaming during sync (best-effort poll if needed).

Additional Context

• CFN support: NO — SynchronizeGatewayTargets is an action, not a CFN resource.
• Control-plane: YES — full action exposed.
• The IAM policies the CLI generates already grant bedrock-agentcore:SynchronizeGatewayTargets for semantic-search-enabled gateways; this issue extends the surface to manual sync.