[Phase 1.3] Temporal configuration + secrets (#11)

## Changes
- `internal/config/config.go` — Env-specific loading (dev/staging/prod), validation, in-cluster detection
- `internal/config/config_test.go` — 11 tests covering defaults, env override, TLS, prod gates
- `k8s/secrets.enc.yaml` — SOPS-encrypted Secret (anthropic key, memory JWT, temporal postgres pw)

## Validation
- 11 config tests pass
- Full test suite passes (`go test ./...`)
- `go build ./...` clean
- SOPS encryption verified (age key)

.gitignore

@@ -7,3 +7,7 @@
 starter
 worker
 poimen
+
+# Compiled binaries
+poimen-worker
+poimen-api