Add PostHog consent integration and extract integration plugin system

Add PostHog opt-in/opt-out consent support mirroring the existing Google
Consent Mode integration: database column, GraphQL field, console UI
toggle, and client-side posthog-js calls.

Extract both GCM and PostHog logic from CookieBannerClient into a
ConsentIntegration plugin interface so future integrations can be added
without modifying the client core.

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/server/api/console/v1/cookie_banner_resolvers.go

@@ -472,6 +472,7 @@ func (r *mutationResolver) UpdateCookieCategory(ctx context.Context, input types
 			Slug:             input.Slug,
 			Description:      input.Description,
 			GCMConsentTypes:  gcmConsentTypes,
+			PostHogConsent:   input.PosthogConsent,
 		},
 	)
 	if err != nil {

pkg/server/api/console/v1/graphql/cookie_banner.graphql

@@ -124,6 +124,7 @@ type CookieCategory implements Node {
     kind: CookieCategoryKind!
     rank: Int!
     gcmConsentTypes: [String!]!
+    posthogConsent: Boolean!
 
     cookies(
         first: Int
@@ -310,6 +311,7 @@ input UpdateCookieCategoryInput {
     slug: String
     description: String
     gcmConsentTypes: [String!]
+    posthogConsent: Boolean
 }
 
 input DeleteCookieCategoryInput {

pkg/server/api/console/v1/types/cookie_category.go

@@ -76,6 +76,7 @@ func NewCookieCategory(c *coredata.CookieCategory) *CookieCategory {
 		Kind:            c.Kind,
 		Rank:            c.Rank,
 		GcmConsentTypes: gcmConsentTypes,
+		PosthogConsent:  c.PostHogConsent,
 		CreatedAt:       c.CreatedAt,
 		UpdatedAt:       c.UpdatedAt,
 	}