feat(smtp): initial implementation — SMTP client with no-op fallback and template rendering (v1.0.0)

Introduces code.nochebuena.dev/einherjar/smtp — the email delivery starter for the
Einherjar framework. New module with no micro-lib counterpart. Pure stdlib — no
external dependencies beyond contracts and core.

Interfaces (CT-6: one TypeSpec per file):
- Sender — Send(ctx context.Context, msg Message) error
- Component — lifecycle.Component + observability.Checkable + Sender
- Message — To, CC, BCC, ReplyTo, Subject, Body, ContentType, Attachments
- Attachment — Name, ContentType string; Data io.Reader (consumed once on Send)
- Template — wraps html/template for email rendering

Implementation:
- New(logger, cfg) Component — returns noopClient when cfg.Host is empty;
  SMTP absence must never block a transaction (e.g. account creation)
- noopClient: all lifecycle and Send methods return nil; Send logs Warn;
  Priority LevelDegraded; Name "smtp"
- smtpClient: OnInit/OnStart/OnStop are no-ops (stateless stdlib client);
  HealthCheck: TCP dial to Host:Port; Priority LevelDegraded
- Send: buildRawMessage → netsmtp.SendMail; BCC passed in SMTP envelope
  (RCPT TO) but never written to message headers (RFC 5321/5322 compliance)
- buildRawMessage: plain message without attachments; multipart/mixed with
  quoted-printable body + base64 attachments when Attachments non-empty;
  multipart.NewWriter created first to obtain boundary before headers are written
- ParseFS(fsys, patterns...) (*Template, error) — wraps html/template.ParseFS
- Template.Render(name, data) (string, error) — executes named template
- net/smtp aliased as netsmtp to avoid package-name collision in package smtp

Config (EINHERJAR_SMTP_* env vars):
  Host, Port(587), User, Password, From

- Component interface embeds observability.Identifiable; identifiable.go implements
  ModulePath and ModuleVersion on both smtpClient and noopClient via
  runtime/debug.ReadBuildInfo() — prints in launcher banner

README.md

@@ -0,0 +1,127 @@
+# einherjar/smtp
+
+[![version](https://img.shields.io/badge/version-v1.0.0-5C4EE5?style=flat-square)](https://code.nochebuena.dev/einherjar/smtp)
+[![license](https://img.shields.io/badge/license-AGPL--3.0-22863A?style=flat-square)](LICENSE)
+[![go](https://img.shields.io/badge/Go-1.26+-00ADD8?style=flat-square&logo=go&logoColor=white)](https://go.dev)
+[![health](https://img.shields.io/badge/health-degraded-E36209?style=flat-square)]()
+
+> A raven sent from Valhalla reaches its destination. The sender does not wait at the window.
+
+`code.nochebuena.dev/einherjar/smtp` is the email sender component of the Einherjar framework. It is built entirely on the Go standard library (`net/smtp`, `mime/multipart`, `html/template`) with no external dependencies. When `EINHERJAR_SMTP_HOST` is empty, `New` returns a silent no-op — email absence never blocks a transaction, user registration, or order placement. Health priority is `LevelDegraded`.
+
+---
+
+## Usage
+
+### Setup
+
+```go
+import "code.nochebuena.dev/einherjar/smtp"
+
+mailer := smtp.New(logger, smtp.DefaultConfig())
+launcher.Append(mailer)   // OnInit verifies credentials; OnStop is a no-op
+health.Register(mailer)   // dial check; LevelDegraded
+```
+
+When `cfg.Host` is empty, `New` returns a no-op that logs every `Send` call at debug level and always returns nil. No code changes are needed between environments.
+
+### Sending a plain-text email
+
+```go
+err := mailer.Send(ctx, smtp.Message{
+    To:      []string{"user@example.com"},
+    Subject: "Welcome to the service",
+    Body:    "Your account is ready.",
+})
+```
+
+### Sending HTML with attachments
+
+```go
+err := mailer.Send(ctx, smtp.Message{
+    To:          []string{"user@example.com"},
+    CC:          []string{"support@example.com"},
+    BCC:         []string{"audit@example.com"},   // envelope only — never in headers
+    Subject:     "Your invoice",
+    Body:        renderedHTML,
+    ContentType: "text/html",
+    Attachments: []smtp.Attachment{
+        {
+            Name:        "invoice.pdf",
+            ContentType: "application/pdf",
+            Data:        pdfReader,   // consumed once; do not reuse
+        },
+    },
+})
+```
+
+### Template rendering
+
+Template rendering is intentionally separate from `Send`. Render to a string first, then assign to `Message.Body`. This keeps the transport and rendering concerns independent.
+
+```go
+tmpl, err := smtp.ParseFS(os.DirFS("templates"), "*.html")
+if err != nil {
+    return err
+}
+
+body, err := tmpl.Render("welcome.html", map[string]any{
+    "Name": user.Name,
+    "URL":  activationURL,
+})
+if err != nil {
+    return err
+}
+
+err = mailer.Send(ctx, smtp.Message{
+    To:          []string{user.Email},
+    Subject:     "Activate your account",
+    Body:        body,
+    ContentType: "text/html",
+})
+```
+
+---
+
+## Environment variables
+
+| Variable | Required | Default | Description |
+|---|---|---|---|
+| `EINHERJAR_SMTP_HOST` | No | `""` | SMTP host. Empty → no-op sender |
+| `EINHERJAR_SMTP_PORT` | No | `587` | SMTP port |
+| `EINHERJAR_SMTP_USER` | No | `""` | Auth username |
+| `EINHERJAR_SMTP_PASSWORD` | No | `""` | Auth password |
+| `EINHERJAR_SMTP_FROM` | No | `""` | Default From address |
+
+---
+
+## Dependency graph
+
+```
+contracts  (zero dependencies)
+    ↑
+  core
+    ↑
+smtp  (contracts, core, stdlib only)
+    ↑
+  your app
+```
+
+No external dependencies beyond the Go standard library.
+
+---
+
+## Verification
+
+```bash
+cd smtp/
+go build ./...
+go vet ./...
+go test ./...
+gofmt -l .
+```
+
+---
+
+> *The message matters. The raven is only the path.*
+> *Make the path reliable. Do not let it stop the battle.*