[Docs] Add issue templates (bug/feature/task)

[JasonEran]

Epic: #8

Goal

Standardize issue creation so tasks are consistently scoped and testable.

Acceptance Criteria

• .github/ISSUE_TEMPLATE contains task + bug + feature templates.
• Templates include acceptance criteria + validation steps.

[JasonEran]

Final Evidence

Completed by PR #51:

• [v2.3][Process] Complete templates + Mermaid class diagrams #51
• Merge commit: 3ea5247

Acceptance mapping:

• .github/ISSUE_TEMPLATE now includes bug + feature + task templates.
• Templates include acceptance criteria and validation steps.