feat: initialize project structure and error types

- go.mod with github.com/dailz/go-kv, Go 1.26.3, testify
- config/config.go with WalConfig, Validate() with checked arithmetic
- errors.go with sentinel errors (ErrCommitUnknown, ErrWriteStopped, etc.)
- wal/constants.go with all WAL format constants and enums
- wal/header.go with WAL File Header encode/decode (CRC32 IEEE)
- wal/record.go with Physical Record codec, block boundary, SplitIntoRecords
- wal/entry.go with WAL Entry codec (varint keys/values, OpType, ValueKind)
- wal/sequence.go with SequenceManager (atomic, CAS, overflow-safe)
- manifest/manifest.go with MANIFEST stub (Load/Save atomic)
- manifest/current.go with CURRENT file (WriteCurrent/ReadCurrent)
- Comprehensive tests for all modules
- .golangci.yml configuration

.golangci.yml

@@ -0,0 +1,24 @@
+run:
+  timeout: 5m
+
+linters:
+  enable:
+    - errcheck
+    - govet
+    - staticcheck
+    - unused
+    - gosimple
+    - ineffassign
+    - typecheck
+    - misspell
+    - gofmt
+
+linters-settings:
+  errcheck:
+    check-type-assertions: true
+  govet:
+    enable-all: true
+
+issues:
+  max-issues-per-linter: 50
+  max-same-issues: 5