Add project documentation and update workflow plan

Adds AGENTS.md, DESIGN.md, and docs/* covering architecture,
conventions, decisions, checklists, branching, release process,
and prompts. Updates README and workflow-feedback-plan to reflect
the decoupled GroupName nomination model.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/PROMPTS.md

@@ -0,0 +1,154 @@
+# Reusable Engineering Prompts
+
+Use these prompts with [../AGENTS.md](../AGENTS.md),
+[PROJECT.md](PROJECT.md), [ARCHITECTURE.md](ARCHITECTURE.md), and
+[CONVENTIONS.md](CONVENTIONS.md).
+
+## Feature Development
+
+```text
+Act as a senior engineer in the VTuber Star Awards repository.
+
+Objective:
+Implement <feature>.
+
+Context:
+- Product goal: <goal>
+- Relevant docs: docs/PROJECT.md, docs/ARCHITECTURE.md, docs/CONVENTIONS.md
+- Relevant files: <files>
+
+Requirements:
+- <requirement>
+
+Non-goals:
+- <non-goal>
+
+Before coding:
+- Inspect current frontend/backend behavior.
+- Confirm the backend/admin source of truth.
+- Ask concise questions if confidence is below 95%.
+
+After coding:
+- Run npm run build, dotnet build Backend/Backend.csproj --configuration Release,
+  git diff --check, and targeted manual checks.
+- Summarize changed files, validation, and residual risk.
+```
+
+## Bug Investigation
+
+```text
+Investigate this bug before changing code.
+
+Observed behavior:
+<observed behavior>
+
+Expected behavior:
+<expected behavior>
+
+Evidence:
+<logs, screenshots, steps, URLs>
+
+Task:
+- Reproduce or reason from available evidence.
+- Identify the most likely root cause.
+- Locate affected frontend, backend, database, or deployment code.
+- Propose the smallest maintainable fix.
+- Implement only after the cause is understood.
+- Add or describe regression validation.
+```
+
+## Admin UI Audit
+
+```text
+Audit this admin page for logical structure, all-at-a-glance clarity, duplicate
+controls, permissions, and component-level behavior.
+
+Scope:
+<route or files>
+
+Expectations:
+- Preserve backend/admin truth.
+- Split oversized Vue files where useful.
+- Keep operational UI dense and scannable.
+- Verify the page in browser when practical.
+- Report validation and any remaining risks.
+```
+
+## Architecture Review
+
+```text
+Review the architecture of <system or module>.
+
+Use:
+- docs/PROJECT.md
+- docs/ARCHITECTURE.md
+- docs/DECISIONS.md
+- Relevant source files
+
+Focus on:
+- Boundary clarity.
+- Backend/admin source of truth.
+- Data ownership.
+- Failure modes.
+- Security and authorization assumptions.
+- Operational complexity.
+- Maintainability over the next release cycle.
+
+Return findings ordered by severity, then trade-offs and recommended ADR updates.
+```
+
+## Security Review
+
+```text
+Perform a security review of <scope>.
+
+Focus on:
+- Authentication.
+- Authorization.
+- Input validation.
+- Output encoding.
+- Secrets handling.
+- Data exposure.
+- Demo or seed behavior.
+- Logging of sensitive data.
+- SSRF, injection, XSS, CSRF, path traversal, and insecure deserialization where relevant.
+
+For each finding include impact, exploitability, evidence, recommended fix, and
+validation strategy.
+```
+
+## Documentation Update
+
+```text
+Improve documentation for <area>.
+
+Goals:
+- Make setup and maintenance easier.
+- Preserve existing project-specific docs.
+- Remove outdated or duplicated information.
+- Add links to authoritative docs.
+- Avoid placeholders and invented policy.
+
+Validate:
+- Links are correct.
+- Commands match the repository.
+- The document is useful to a new contributor.
+```
+
+## Release Verification
+
+```text
+Verify the latest release for VTuber Star Awards.
+
+Scope:
+<commit, PR, or change summary>
+
+Check:
+- CI/deploy status when available.
+- https://award.noveria.net/api/health
+- https://award.noveria.net/api/health/database
+- Frontend asset version when relevant.
+- One targeted public or authenticated workflow affected by the change.
+
+Return confirmed facts, failures, and residual risk.
+```