[Feature] Refactor stack selection into dependency-aware flow

[b-jonathan]

Title: [Feature] Refactor stack selection into dependency-aware flow

Type: Feature

Description:
Currently the CLI prompts for frontend, backend, and database stacks using static lists. Some stack combinations may be incompatible. Refactor selection so options are dependency-aware (e.g., after selecting a backend, only compatible databases are shown).

Location:

• File: internal/cli/root.go
• Approx line: 140

Steps to reproduce (current behavior):

1. Run taco init in interactive mode.
2. Select frontend and backend from static lists.
3. Observe database options are not filtered by backend capabilities.

Expected result (after change):

• Stack selection UI presents only compatible options (backend -> allowed DBs, etc.).
• Less chance of generating incompatible scaffolding.

Environment:

• CLI interactive flow (survey prompts)

Checks:

• I searched existing issues
• I included a description and proposed changes

Suggested labels: enhancement, refactor, cli