Rewrite backend in Go with JSON API and JS frontend

Reimplements the Flask app as a Go HTTP API (chi + modernc sqlite) with a
minimal vanilla-JS frontend in web/. Endpoints mirror the original Flask
routes but return JSON instead of HTML.

- auth: login/logout/register/sessioninfo/headerbar with crypto/rand tokens
- entry: paginated feed (single JOIN), create with image scaling
- user: profile, userinfo; delete still a stub
- requireAuth middleware passes uid via context
- notes/api.md documents the API and schema

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go.mod

@@ -0,0 +1,22 @@
+module kver
+
+go 1.25.0
+
+require (
+	github.com/go-chi/chi/v5 v5.3.0
+	golang.org/x/crypto v0.52.0
+	golang.org/x/image v0.41.0
+	modernc.org/sqlite v1.51.0
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/sys v0.45.0 // indirect
+	modernc.org/libc v1.72.3 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
+)