[Feature]: Allow multi script types on same speckit project

[ajsantos-csw]

Problem Statement

Now speckit only generates either powershell or bash scripts. They're stored on .specify/scripts/ and declared on .specify\integrations\speckit.manifest.json. However, for a team that works with different OS's, each team member will have to generate the scripts again by running specify init --here on the project root, so they match the current OS.

Proposed Solution

It makes perfect sense for speckit to generate both types of scripts and then choose the appropriate ones based on the current OS.

Alternatives Considered

No response

Component

Specify CLI (initialization, commands)

AI Agent (if applicable)

None

Use Cases

No response

Acceptance Criteria

• [] Both powershell and bash scripts are generated on specify init.
• [] The speckit.manifest.json maps all scripts.
• [] The users can checkout a initialized speckit project and run specify commands and speckit workflow prompts without needed to adapt anything, independently of what OS they're using.

Additional Context

No response