docs(copilot): align workflow with develop_1.0 [#38]

[seokheehan]

Summary

Align .github/copilot-instructions.md with the repository's finalized development and release branch policy.

Changes

• Document develop_1.0 as the default branch for ongoing development and integration.
• Document main as the branch for release-qualified delivery.
• Target implementation pull requests at develop_1.0.
• Document reviewed release promotion from develop_1.0 to main.
• Clarify the short-lived lifecycle of Issue-specific topic branches.
• Preserve the existing review, CI, and no-direct-push requirements.

Validation

• git diff --check
• Verified the required branch-policy wording and absence of stale branch references.
• VS Code reported no errors for the updated file.

Closes #38

[chanjeong-lge]

looks good

[basheerFZ]

looks good