First interactive deploy of a fresh project fails: "Stack selection is ambiguous, please choose a specific stack for import"

[jesseturner21]

Describe the bug

The very first agentcore deploy (interactive TUI mode) on a freshly created project fails immediately after synth:

[13:41:25] STEP: Publish assets
[13:41:25] [trace] CDK_TOOLKIT_I1001: Starting Synthesis ...
[13:41:25] [debug] CDK_ASSEMBLY_I0150: --app points to a cloud assembly, so we bypass synth
[13:41:25] [info] CDK_TOOLKIT_I1000: ✨  Synthesis time: 0.01s
[13:41:25] Error: CDK deploy failed: Stack selection is ambiguous, please choose a specific stack for import [AgentCore-clitest-default]
[13:41:25] Status: FAILED

Re-running deploy a second time succeeds, which masks the bug.

To reproduce

1. agentcore create --name clitest
2. cd clitest && agentcore deploy (interactive, no flags)

Root cause

Regression from the #1267 fix (#1659). The TUI deploy flow now scopes its stack selector to the target picker's selection (useDeployFlow.ts builds a PATTERN_MUST_MATCH selector from selectedTargets), and deliberately treats an empty selection as "deploy nothing".

A fresh project has an empty aws-targets.json, so useAwsTargetConfig takes the auto-detect path: it detects the AWS account/region and writes a default target — but unlike the single-pre-configured-target and multi-target-picker paths, it never populates selectedTargetIndices. DeployScreen then passes selectedTargets = [] into the deploy flow, producing a PATTERN_MUST_MATCH selector with zero patterns, and toolkit-lib throws NoStacksMatched ("Stack selection is ambiguous...").

On the second run aws-targets.json has one entry, so the single-target path selects index 0 and deploy works — every first deploy of a new project is broken.