feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages
- internal: source, keymap, merge, structconv, bytesutil
- cmd/envc: convert, get, merge
- docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh
- golangci-lint v2 config; tests + fixtures

Co-authored-by: Cursor <cursoragent@cursor.com>

.golangci.yml

@@ -1,13 +1,17 @@
+version: "2"
+
 run:
   timeout: 5m
   tests: true
 
-linters:
-  disable-all: true
+formatters:
   enable:
-    - errcheck
     - gofmt
     - goimports
+
+linters:
+  enable:
+    - errcheck
     - govet
     - ineffassign
     - revive