refactor: adopt portigo infrastructure patterns

Add config package with build-tag-switched dev/prod environments,
structured logging via zerolog, Taskfile for dev workflow, golangci-lint
config, testutil package, and improved DB setup with proper SQLite
pragmas and cleanup. Rename sqlc output package from gen to repository.

Switch to allowlist .gitignore, Alpine+UPX+scratch Dockerfile, and
CI pipeline with test/lint gates before deploy.

.golangci.yml

@@ -0,0 +1,45 @@
+version: "2"
+
+linters:
+  default: standard
+  enable:
+    - errcheck
+    - govet
+    - staticcheck
+    - gosec
+    - bodyclose
+    - sqlclosecheck
+    - misspell
+    - errname
+    - copyloopvar
+
+  settings:
+    staticcheck:
+      checks:
+        - all
+        - "-ST1001" # dot imports
+        - "-ST1003" # naming conventions
+    gosec:
+      excludes:
+        - G104 # unhandled errors — redundant with errcheck
+        - G107 # HTTP requests with variable URLs — expected in a web app
+        - G115 # integer overflow conversion
+        - G301 # directory permissions 0750 — 0755 is standard for data dirs
+        - G404 # weak random — acceptable for game IDs and player IDs
+
+formatters:
+  enable:
+    - gofmt
+    - goimports
+
+  settings:
+    goimports:
+      local-prefixes:
+        - github.com/ryanhamamura/c4
+
+issues:
+  exclude-rules:
+    - path: _test\.go
+      linters:
+        - gosec
+        - errcheck