Implement production and development build targets with binary size optimization

- Add LDFLAGS_BASE for version info only, LDFLAGS for production (with -s -w optimization), and LDFLAGS_DEV for development
- Create 'build' target (production) that strips symbols, reducing binary size by ~30% (56MB -> 39MB)
- Create 'build-dev' target (development) that keeps debug symbols for profiling
- Update 'docker-build' to pass BUILD_FLAGS="-s -w" for optimized production images
- Create 'docker-build-dev' target that builds development images with notifier:latest-dev tag and no optimization
- Update Dockerfile to accept and use BUILD_FLAGS argument in build stage
- All targets now clearly indicate their optimization level in output messages

Dockerfile

@@ -5,6 +5,7 @@ FROM golang:1.24-alpine AS builder
 ARG VERSION=dev
 ARG GIT_COMMIT=unknown
 ARG BUILD_TIME=unknown
+ARG BUILD_FLAGS="-s -w"
 
 # Install build dependencies including protoc
 RUN apk add --no-cache git make protobuf protobuf-dev
@@ -30,7 +31,7 @@ RUN make proto-gen
 
 # Build binary with version information
 RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo \
-    -ldflags "-X main.Version=${VERSION} -X main.GitCommit=${GIT_COMMIT} -X main.BuildTime=${BUILD_TIME}" \
+    -ldflags "-X main.Version=${VERSION} -X main.GitCommit=${GIT_COMMIT} -X main.BuildTime=${BUILD_TIME} ${BUILD_FLAGS}" \
     -o server ./cmd/server
 
 # Runtime stage