Implement local build from manifest for sh1pt build --from

[KCDaemon]

Part of #133.

The docs describe sh1pt build --from <input> as a primary CLI path, but the current local path flow only prints a stub. This issue tracks making the local project path flow read sh1pt.config.*, select enabled targets, and invoke target adapter builds with a real build context.

Scope:

• Load local sh1pt.config.{json,js,mjs,ts}.
• Support selecting targets with --target.
• Write build artifacts under .sh1pt/build/<channel>/<target>.
• Keep cloud/git/url support out of scope for now.