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/branching.md

@@ -0,0 +1,76 @@
+# Branching Strategy
+
+This repository uses a simple trunk-based model with short-lived branches and
+`main` as the deploy branch.
+
+For delivery workflow, see [workflow.md](workflow.md). For PR expectations, see
+[CONVENTIONS.md](CONVENTIONS.md#git-and-prs).
+
+## Default Model
+
+```mermaid
+gitGraph
+    commit id: "main"
+    branch docs-change
+    checkout docs-change
+    commit id: "work"
+    commit id: "validate"
+    checkout main
+    merge docs-change
+    commit id: "deploy"
+```
+
+## Branch Types
+
+| Type | Pattern | Purpose |
+| --- | --- | --- |
+| Feature | `feature/<short-description>` | New user-facing or system capability. |
+| Bug fix | `fix/<short-description>` | Defect correction. |
+| Refactor | `refactor/<short-description>` | Behavior-preserving structural work. |
+| Documentation | `docs/<short-description>` | Documentation-only changes. |
+| Chore | `chore/<short-description>` | Tooling or maintenance work. |
+| AI-assisted local work | `codex/<short-description>` | Short-lived Codex branch when branch creation is useful. |
+| Hotfix | `hotfix/<short-description>` | Urgent production correction. |
+
+## Main Branch
+
+`main` should remain deployable.
+
+Minimum expectations:
+
+- required checks pass;
+- risky migrations and config changes are documented;
+- production-impacting changes include validation evidence;
+- direct pushes are limited to maintainers or automation.
+
+## Feature Branches
+
+- Keep scope focused.
+- Rebase or merge from `main` according to reviewer preference.
+- Delete branches after merge.
+- Avoid stacking unrelated changes.
+- Do not include generated build output or handoff artifacts.
+
+## Commit Messages
+
+Use short imperative subjects that describe the outcome.
+
+Examples:
+
+- `Fix team profile auth recovery`
+- `Refine admin risk workspace`
+- `Document engineering workflow`
+
+Use a longer body when context, migration notes, or validation evidence is
+important for future archaeology.
+
+## Hotfixes
+
+Hotfixes should restore production safely:
+
+1. Branch from the deployed commit or current `main`.
+2. Apply the smallest safe fix.
+3. Validate the failing path.
+4. Deploy.
+5. Merge back to `main`.
+6. Add follow-up cleanup or tests when the hotfix intentionally stayed narrow.