Consolidate connector provider dispatch behind a typed *Registry

The console previously dispatched per-provider logic through a fan of
init()-side-effect maps (driver names, OAuth2 metadata, probe URLs,
display names, settings switches), spread across pkg/connector,
pkg/accessreview/drivers and the console v1 resolvers. Adding a new
provider required edits in every one of those places and a corresponding
switch arm in CreateConnectorRequest. The same per-provider knowledge
also leaked into Helm templates as hand-rolled environment-variable
blocks per connector.

This commit collapses the dispatch surface into a single typed
*provider.Registry. The registry is constructed once by
NewBuiltinRegistry at probod startup and threaded as an explicit
dependency into every consumer (accessreview service, console v1
resolver, OAuth2 wiring). There is no package-level state. Each
provider lives in one file under pkg/connector/provider/ that exposes
a private xxxRegistration() *Registration constructor; NewBuiltinRegistry
enumerates them.

CreateConnectorRequest loses its per-provider settings fields and
takes a single RawSettings json.RawMessage produced by the
per-provider MarshalSettings closure. The 1Password SCIM bridge URL
is validated at create time (http(s) scheme + non-empty host) so a
malformed value fails fast at the resolver boundary. The Helm chart
gains probo.connectorEnv and probo.connectorSecretEntries templates
so adding a connector requires zero Helm changes. Access-review name
resolution moves into the same Registration value to keep one
authoritative dispatch table.

Tests cover every Registration (DisplayName, NewDriver wired),
Register error paths (nil, empty Provider, empty DisplayName,
duplicate), All / ProviderDisplayName / ProviderOAuth2Scopes /
ProbeURL hit and miss paths, the ApplyOAuth2Defaults templating and
PKCE branches, and ConnectorSettings[T] round-trip plus malformed-JSON
error path. The pre-refactor ApplyProviderDefaults test in
pkg/connector is replaced by the equivalent in
pkg/connector/provider.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/connector/provider/apply_test.go

@@ -0,0 +1,88 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package provider_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.probo.inc/probo/pkg/connector"
+	"go.probo.inc/probo/pkg/connector/provider"
+)
+
+// TestApplyOAuth2Defaults_AuthURLTemplating verifies that operator-supplied
+// AuthURLParams (for example Vercel's "{integration_slug}") are substituted
+// into the static provider AuthURL when the connector is initialized.
+// Providers without placeholders are unaffected.
+func TestApplyOAuth2Defaults_AuthURLTemplating(t *testing.T) {
+	t.Parallel()
+
+	t.Run("placeholder is substituted when AuthURLParams is supplied", func(t *testing.T) {
+		t.Parallel()
+
+		r := provider.NewBuiltinRegistry()
+		c := &connector.OAuth2Connector{
+			ClientID:     "id",
+			ClientSecret: "secret",
+			AuthURLParams: map[string]string{
+				"integration_slug": "acme",
+			},
+		}
+
+		// VERCEL uses a templated AuthURL with the
+		// "{integration_slug}" placeholder.
+		r.ApplyOAuth2Defaults("VERCEL", "https://example.com/cb", c)
+
+		assert.Equal(t, "https://vercel.com/integrations/acme/new", c.AuthURL)
+		assert.Equal(t, "https://api.vercel.com/v2/oauth/access_token", c.TokenURL)
+	})
+
+	t.Run("placeholder remains literal when AuthURLParams is empty", func(t *testing.T) {
+		t.Parallel()
+
+		r := provider.NewBuiltinRegistry()
+		c := &connector.OAuth2Connector{
+			ClientID:     "id",
+			ClientSecret: "secret",
+		}
+
+		r.ApplyOAuth2Defaults("VERCEL", "https://example.com/cb", c)
+
+		// No substitution requested; the placeholder is preserved
+		// verbatim so a misconfiguration is visible at the
+		// authorization step rather than silently masked.
+		assert.Equal(t, "https://vercel.com/integrations/{integration_slug}/new", c.AuthURL)
+	})
+}
+
+// TestApplyOAuth2Defaults_PKCEDefaults asserts that the registered
+// PAGERDUTY provider defaults flip RequiresPKCE on so the downstream
+// Initiate/Complete flow generates a verifier and replays it.
+func TestApplyOAuth2Defaults_PKCEDefaults(t *testing.T) {
+	t.Parallel()
+
+	for _, p := range []string{"PAGERDUTY"} {
+		t.Run(p, func(t *testing.T) {
+			t.Parallel()
+
+			r := provider.NewBuiltinRegistry()
+			c := &connector.OAuth2Connector{ClientID: "id", ClientSecret: "secret"}
+			r.ApplyOAuth2Defaults(p, "https://example.com/cb", c)
+			assert.True(t, c.RequiresPKCE,
+				"provider %s must enable PKCE so Initiate generates a verifier", p)
+		})
+	}
+}