docs: add GIT_WORKFLOW.md branching and commit policy

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

GIT_WORKFLOW.md

@@ -0,0 +1,60 @@
+# Git workflow
+
+This project uses a lightweight trunk-based workflow. It's a solo/small-team
+project, so the goal is just enough process to keep `main` deployable and the
+history readable — not ceremony for its own sake.
+
+## Branches
+
+- `main` — always deployable. Nothing is committed to `main` directly except
+  by merging a branch through the steps below.
+- `feat/<short-name>` — new functionality (e.g. `feat/gif-picker`).
+- `fix/<short-name>` — bug fixes (e.g. `fix/expired-proposal-redirect`).
+- `refactor/<short-name>` — internal changes with no user-facing behavior
+  change (e.g. `refactor/ui-ux-shadcn`).
+- `chore/<short-name>` — tooling, deps, config.
+
+Branch names are kebab-case and describe the change, not the ticket number
+(there's no issue tracker yet).
+
+## Commits
+
+Follow [Conventional Commits](https://www.conventionalcommits.org/):
+
+```
+<type>(<optional scope>): <summary, imperative mood, no trailing period>
+
+<optional body: why, not what>
+```
+
+Types: `feat`, `fix`, `refactor`, `style`, `docs`, `chore`, `test`.
+
+- Keep commits small and focused — one logical change per commit.
+- Write the summary in the imperative ("add", not "added"/"adds").
+- Explain *why* in the body when the reason isn't obvious from the diff.
+
+## Merging
+
+- Rebase your branch on `main` before merging (`git fetch && git rebase
+  origin/main`) to keep history linear — don't merge `main` into a feature
+  branch.
+- Squash-merge feature/fix/chore branches into `main` so each lands as one
+  commit. Larger `refactor/*` branches with independently meaningful commits
+  may use a regular merge instead of squashing, if keeping the granular
+  history is genuinely useful for a future bisect.
+- Delete the branch after it's merged.
+- Never force-push `main`. Force-pushing a feature branch you own (after a
+  rebase) is fine; never force-push a branch someone else might be using.
+
+## Tags / releases
+
+Tag production releases as `v<major>.<minor>.<patch>` (semver) once this
+project has a deployment cadence worth marking. Not required for every merge.
+
+## What not to commit
+
+- Anything in `.gitignore` (`.env`, `/data`, `.next`, `node_modules`, prisma
+  migration SQL under `prisma/migrations/*/migration.sql`).
+- Generated/build artifacts.
+- Secrets of any kind, even in comments or examples — use `.env.example` for
+  documenting required variables.