Add OAuth files - authentication system

Migrated from app/:
- oauth.go - OAuthManager, config loading, handle/DID resolution
- oauth_session.go - SessionStore, encrypted cookies, token storage
- oauth_middleware.go - RequireAuth middleware, token refresh
- oauth_handlers.go - Login, callback, logout, JWKS endpoints

Changed *DB to *shared.DB, using shared.StringValue/NullableString helpers.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.mod

@@ -2,16 +2,75 @@ module github.com/1440news/dashboard
 
 go 1.24.0
 
-require github.com/1440news/shared v0.0.0
+require (
+	github.com/1440news/shared v0.0.0
+	github.com/haileyok/atproto-oauth-golang v0.0.3
+	github.com/lestrrat-go/jwx/v2 v2.1.6
+)
 
 require (
+	github.com/bluesky-social/indigo v0.0.0-20250616202859-d4516ea1d6cf // indirect
+	github.com/carlmjohnson/versioninfo v0.22.5 // indirect
+	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/goccy/go-json v0.10.3 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang-jwt/jwt/v5 v5.2.2 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
+	github.com/hashicorp/go-retryablehttp v0.7.5 // indirect
+	github.com/hashicorp/golang-lru v1.0.2 // indirect
+	github.com/ipfs/bbloom v0.0.4 // indirect
+	github.com/ipfs/go-block-format v0.2.0 // indirect
+	github.com/ipfs/go-cid v0.4.1 // indirect
+	github.com/ipfs/go-datastore v0.6.0 // indirect
+	github.com/ipfs/go-ipfs-blockstore v1.3.1 // indirect
+	github.com/ipfs/go-ipfs-ds-help v1.1.1 // indirect
+	github.com/ipfs/go-ipfs-util v0.0.3 // indirect
+	github.com/ipfs/go-ipld-cbor v0.1.0 // indirect
+	github.com/ipfs/go-ipld-format v0.6.0 // indirect
+	github.com/ipfs/go-log v1.0.5 // indirect
+	github.com/ipfs/go-log/v2 v2.5.1 // indirect
+	github.com/ipfs/go-metrics-interface v0.0.1 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/pgx/v5 v5.7.5 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/jbenet/goprocess v0.1.4 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
+	github.com/lestrrat-go/blackmagic v1.0.3 // indirect
+	github.com/lestrrat-go/httpcc v1.0.1 // indirect
+	github.com/lestrrat-go/httprc v1.0.6 // indirect
+	github.com/lestrrat-go/iter v1.0.2 // indirect
+	github.com/lestrrat-go/option v1.0.1 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/minio/sha256-simd v1.0.1 // indirect
+	github.com/mr-tron/base58 v1.2.0 // indirect
+	github.com/multiformats/go-base32 v0.1.0 // indirect
+	github.com/multiformats/go-base36 v0.2.0 // indirect
+	github.com/multiformats/go-multibase v0.2.0 // indirect
+	github.com/multiformats/go-multihash v0.2.3 // indirect
+	github.com/multiformats/go-varint v0.0.7 // indirect
+	github.com/opentracing/opentracing-go v1.2.0 // indirect
+	github.com/polydawn/refmt v0.89.1-0.20221221234430-40501e09de1f // indirect
+	github.com/segmentio/asm v1.2.0 // indirect
+	github.com/spaolacci/murmur3 v1.1.0 // indirect
+	github.com/whyrusleeping/cbor-gen v0.2.1-0.20241030202151-b7a6831be65e // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.46.1 // indirect
+	go.opentelemetry.io/otel v1.29.0 // indirect
+	go.opentelemetry.io/otel/metric v1.29.0 // indirect
+	go.opentelemetry.io/otel/trace v1.29.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
+	go.uber.org/zap v1.26.0 // indirect
 	golang.org/x/crypto v0.47.0 // indirect
 	golang.org/x/sync v0.19.0 // indirect
+	golang.org/x/sys v0.40.0 // indirect
 	golang.org/x/text v0.33.0 // indirect
+	golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028 // indirect
+	lukechampine.com/blake3 v1.2.1 // indirect
 )
 
 replace github.com/1440news/shared => ../shared