feat: add --diff flag to deploy command

[notgitika]

Description

Adds a --diff flag to agentcore deploy that runs cdk diff and displays a structured summary of infrastructure changes without actually deploying. In interactive (TUI) mode, users can also toggle the diff view with Ctrl+D during a normal deploy.

What this includes:

1. CLI plumbing — New --diff option registered on the deploy command, routed to both CLI and TUI code paths
2. CDK IoHost data pipe — Extended setOnRawMessage callback to pass structured data from CDK messages (not just text), enabling access to parsed diff objects
3. Diff execution in deploy actions — Early-return path in handleDeploy() that calls toolkitWrapper.diff(), listens for CDK diff event codes (I4002 per-stack, I4001 summary), and skips deployment
4. Diff-aware logging — New logDiff() method on ExecLogger that strips ANSI codes and writes formatted diff output to the log file
5. Diff parser + TUI component — parseStackDiff() and parseDiffResult() parse CDK structured data into typed sections (Resources, Outputs, etc.) with add/modify/remove changes; DiffSummaryView renders a scrollable, color-coded diff view with security warnings
6. Deploy screen integration — useDeployFlow adds diff-mode effect and lazy requestDiff(); DeployScreen renders DiffSummaryView, supports Ctrl+D toggle, and adjusts UI for diff mode

Related Issue

Closes #75

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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