Add CLAUDE.md and Gitea CI workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test -race -count=1 ./...

CLAUDE.md

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+# CLAUDE.md — httpx
+
+## Commands
+
+```bash
+go build ./...                          # compile
+go test ./...                           # all tests
+go test -race ./...                     # tests with race detector
+go test -v -run TestName ./package/     # single test
+go vet ./...                            # static analysis
+```
+
+## Architecture
+
+- **Module**: `git.codelab.vc/pkg/httpx`, Go 1.24, zero external dependencies
+- **Core pattern**: middleware is `func(http.RoundTripper) http.RoundTripper`
+- **Chain assembly order** (client.go): Logging → User MW → Retry → CB → Balancer → Transport
+  - Retry wraps CB+Balancer so each attempt can hit a different endpoint
+- **Circuit breaker** is per-host (`sync.Map` of host → Breaker)
+- **Sentinel errors**: canonical values live in sub-packages, root package re-exports as aliases
+- **balancer.Transport** returns `(Middleware, *Closer)` — Closer must be tracked for health checker shutdown
+- **Client.Close()** stops the health checker goroutine
+
+## Conventions
+
+- Functional options for all configuration
+- Test helpers: `mockTransport(fn)` wrapping `middleware.RoundTripperFunc`
+- No external test frameworks — stdlib only
+- Thread safety required (`sync.Mutex`/`atomic`)
+- `internal/clock` for deterministic time testing