chore: integrate AI development platform into HLL Vietnam project

ai/prompts/plan-feature.md

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+# Plan Feature Prompt
+
+Use this prompt when the orchestrator needs to transform a repository request into implementation-ready tasks.
+
+## Prompt
+
+Analyze the HLL Vietnam repository before proposing any implementation work.
+
+Required behavior:
+
+1. Read `AGENTS.md`.
+2. Read `ai/repo-context.md`.
+3. Read `ai/architecture-index.md`.
+4. Review only the files directly related to the request.
+5. Produce a small, safe task breakdown.
+6. Do not invent product features outside the request.
+7. Keep branding, frontend stack and planned Python backend consistent with the repository rules.
+
+Task output rules:
+
+- Use `ai/task-template.md`.
+- Keep tasks small and verifiable.
+- Prefer one task when the work is very small.
+- Add clear `Files to Read First`.
+- Add clear `Expected Files to Modify`.
+- Include explicit validation steps.