Upgrade Relay to v20.1.1 and unify compiler config

Consolidate the two per-app relay configs (console and trust)
into a single multi-project relay.config.json at the repo root
with three projects: core, iam, and trust. Bump all relay
packages from v19 to v20.1.1 and move relay-compiler to the
root devDependencies. Replace per-workspace relay scripts with
a single root-level npm run relay command and update the
GNUmakefile, CI workflows, and docs accordingly.

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

GNUmakefile

@@ -221,17 +221,19 @@ bin/probod-bootstrap:
 @probo/emails:
 	$(NPM) --workspace $@ run build
 
+.PHONY: relay
+relay:
+	$(NPM) run relay
+
 .PHONY: @probo/console
 @probo/console: NODE_ENV=production
-@probo/console:
-	$(NPM) --workspace $@ run relay
+@probo/console: relay
 	$(NPM) --workspace $@ run check
 	$(NPM) --workspace $@ run build
 
 .PHONY: @probo/trust
 @probo/trust: NODE_ENV=production
-@probo/trust:
-	$(NPM) --workspace $@ run relay
+@probo/trust: relay
 	$(NPM) --workspace $@ run check
 	$(NPM) --workspace $@ run build
 
@@ -244,8 +246,7 @@ generate: pkg/server/api/connect/v1/schema/schema.go \
 	pkg/server/api/trust/v1/types/types.go \
 	pkg/server/api/mcp/v1/server/server.go \
 	pkg/server/api/mcp/v1/types/types.go
-	$(NPM) --workspace @probo/console run relay
-	$(NPM) --workspace @probo/trust run relay
+	$(NPM) run relay
 
 pkg/server/api/connect/v1/schema/schema.go \
 pkg/server/api/connect/v1/types/types.go \