## Why

WhereWoof is a return-item tag platform: buyers get pre-coded QR/NFC tags, a finder scans the tag on a lost item and sees how to return it. The product plan (`where_woof.md`) is settled; nothing of it is buildable yet. This change creates the front-end foundation — the GOAT (Go + HTMX + Alpine + Tailwind + Postgres) app that carries the owner-facing experience: tag setup, account, and the public tag page.

## What Changes

- New Go application in `frontend/` (Go `net/http`, HTMX, Alpine.js, Tailwind via CDN) talking to **Postgres** via `pgx`/`sqlc`.
- Shared database schema (`db/schema.sql`): `users`, `tags`, `scans` tables. Laravel will own migrations later; until then `schema.sql` is the source of truth.
- **User auth**: register / login / logout with email + password, session cookie.
- **Tag management (account CRUD)**: add a tag to the account by entering its `tag_code`, list my tags, edit details (item type, description, photo URL, phone, address, notes), remove a tag. Limit of 20 tags per account enforced.
- **Public tag page** `GET /t/:tag_code`: shows a "not set up yet" prompt when the tag is unset; shows the item's return details (with an edit affordance for a logged-in owner) when set.
- **Scan flow is NOT in this change** (Phase 2): no geolocation, no SMS alerts, no `tel:`/`sms:` links yet — the page renders details only.

## Capabilities

### New Capabilities

- `user-auth`: register, login, logout, session handling for owners.
- `tag-management`: bind a tag_code to an account, list/edit/remove tags, 20-tag limit, item details fields.
- `public-tag-page`: unauthenticated view of a tag by code — setup prompt or return details.
- `database`: shared Postgres schema (users, tags, scans), unique tag codes, tag status lifecycle.

### Modified Capabilities

<!-- none — no existing specs yet -->

## Impact

- **New code**: `frontend/` Go module (main.go, db, handlers, templates, static). No framework beyond stdlib.
- **New schema**: `db/schema.sql` + Postgres database (dev: Supabase Postgres on `.27:5434`).
- **Config**: `DATABASE_URL` env var; port 3020 default.
- **No changes** to admin (Laravel — later phase), deployment (rsync/Caddy — Phase 7), or billing (Phase 5).