feat(devops): improve Docker build caching and add dev workflow targets

- Optimize Dockerfile layer caching with --mount=type=cache for Go modules and npm
- Reorganize Dockerfile layers for better cache hit rates
- Improve .dockerignore organization with categorized comments
- Add Makefile targets: up, down, rebuild-app, restart, ps
- Enhance Makefile help output with categorized sections

Dockerfile

@@ -3,40 +3,39 @@ FROM golang:1.25-alpine AS builder
 
 WORKDIR /app
 
-# Install Node.js, npm, and curl for Tailwind CSS building
-RUN apk add --no-cache nodejs npm curl
+# Install system tools (cached well)
+RUN apk add --no-cache nodejs npm curl git
 
-# Install sqlc
-RUN go install github.com/sqlc-dev/sqlc/cmd/sqlc@latest
+# Install Go tools (cached well)
+RUN --mount=type=cache,target=/root/go/pkg/mod \
+    go install github.com/sqlc-dev/sqlc/cmd/sqlc@latest && \
+    go install github.com/a-h/templ/cmd/templ@latest
 
-# Install templ
-RUN go install github.com/a-h/templ/cmd/templ@latest
-
-# Copy package files and install npm dependencies
+# Copy package files and install npm dependencies (cached unless package.json changes)
 COPY package*.json ./
-RUN npm install
+RUN --mount=type=cache,target=/root/.npm \
+    npm ci
 
-# Copy source code
+# Copy Go mod files (cached unless go.mod changes)
+COPY go.mod go.sum ./
+RUN --mount=type=cache,target=/root/go/pkg/mod \
+    go mod download
+
+# Copy source code (this layer changes frequently)
 COPY . .
 
-# Download dependencies
-RUN go mod tidy
-
-# Generate sqlc code
+# Generate code (only these rebuild on source changes)
 RUN cd internal/database && sqlc generate
-
-# Generate templ code
 RUN cd templates && templ generate
 
-# Build Tailwind CSS and download htmx
+# Build frontend assets (only these rebuild on web/ changes)
 RUN npm run build:css:prod
 RUN npm run postinstall
-
-# Build TypeScript to JavaScript
 RUN npm run build:ts
 
-# Build the application
-RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o main ./cmd/server
+# Build Go binary (cached unless Go files or generated code changes)
+RUN --mount=type=cache,target=/root/go/pkg/mod \
+    CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o main ./cmd/server
 
 # Test runner stage - includes Go runtime and test dependencies
 # This stage is ONLY used for running tests, never deployed to production