Add remaining elements for create kernel app

[archandatta]

This PR competes the remaining work for KERNEL-374

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Note

Implements the kernel create flow with template selection and overwrite prompts, adds deploy/invoke guidance per template, expands tests, and updates README docs.

• Create CLI:
  • Implement kernel create with create.CreateInput type, interactive prompts, and overwrite confirmation via PromptForOverwrite.
  • Copies template files with spinner feedback; handles existing dirs by optional removal.
  • Refactor install flow: InstallDependencies(appPath, CreateInput); prints tailored next steps on failure/missing tools.
• Templates & Commands:
  • Add template key constants and Templates map; provide GetDeployCommand and GetInvokeSample via new Commands matrix per language/template.
  • Normalize language shorthands; expose supported templates per language.
• Tests:
  • Major expansion: creation flow, dependency failure/missing tool paths, overwrite behavior, permissions, invalid combos, shorthands, and template coverage (pkg/create/copy_test.go, updates to cmd/create_test.go).
• Docs:
  • README: add app creation to capabilities, reorder Quick Start (create → login → deploy → invoke), document create flags/templates, and add create examples.

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