feat: initial fire-and-forget telemetry client

Anonymous OSS usage telemetry library with zero third-party deps.

- Send(project, version): fire-and-forget POST to oss.raczylo.com/v1/ping
- Disable() and Wait(timeout) helpers
- Disable via DO_NOT_TRACK, OSS_TELEMETRY_DISABLED, or per-project env
- Failproof: never blocks, never panics, never returns errors
- Hand-written JSON (no encoding/json) and byte-loop validators (no regexp)
- golangci-lint v2 clean, all tests pass with -race

.golangci.yml

@@ -0,0 +1,36 @@
+version: "2"
+
+run:
+  timeout: 2m
+
+linters:
+  default: none
+  enable:
+    - bodyclose
+    - errcheck
+    - errorlint
+    - gocritic
+    - gocyclo
+    - govet
+    - ineffassign
+    - misspell
+    - prealloc
+    - revive
+    - staticcheck
+    - unconvert
+    - unused
+  settings:
+    gocyclo:
+      min-complexity: 12
+    revive:
+      rules:
+        - name: var-naming
+        - name: indent-error-flow
+        - name: superfluous-else
+        - name: unused-parameter
+        - name: redefines-builtin-id
+
+formatters:
+  enable:
+    - gofmt
+    - goimports