fix(build): rebuild sidecar JAR when Kotlin sources change

Without source-file deps on $(SIDECAR_JAR), make never re-ran shadowJar
after a Kotlin edit, so a stale embedded JAR shipped on every install
and the new sidecar code was silently absent at runtime.

Makefile

@@ -8,6 +8,7 @@ BUF := buf
 GO_PACKAGES := ./...
 SIDECAR_JAR := sidecar/build/libs/sidecar-all.jar
 SIDECAR_EMBED := internal/sidecar/assets/sidecar-all.jar
+SIDECAR_SRC := $(shell find sidecar/src -type f \( -name '*.kt' -o -name '*.kts' \) 2>/dev/null) build.gradle.kts settings.gradle.kts
 SANDERLING_BIN := bin/sanderling
 
 DOCS_SRC      := $(shell find docs -type f -name '*.md' -not -path 'docs/_*')
@@ -61,7 +62,7 @@ inspect-dev: $(SIDECAR_EMBED)
 web-typecheck:
 	cd inspect-ui && bun install --frozen-lockfile && bun run typecheck
 
-$(SIDECAR_JAR):
+$(SIDECAR_JAR): $(SIDECAR_SRC)
 	ANDROID_HOME=$(ANDROID_HOME) $(GRADLE) :sidecar:shadowJar
 
 $(SIDECAR_EMBED): $(SIDECAR_JAR)