feat: foundations — canonical types, Parse grammar, env DSNs, health, chains

Phase 1 of the majordomo build:
- llm/ canonical contract (messages, parts, tools, capabilities, streaming,
  Model/Provider, error classification)
- health/ clock-injected tracker (threshold bench, exponential capped
  cooldown, reset-on-success)
- root Registry + Parse (verbatim model ids, inline recursive alias
  expansion with cycle detection, chain dedup), LLM_* env-DSN providers
  (go-llm parity: lazy fallback + eager LoadEnv), health-aware chain
  executor behind the Model interface
- provider/fake scriptable test provider; hermetic test suite incl. the
  trailing-thinking chain and foreman:// env loading
- ADRs 0001-0008, CLAUDE.md, README (honest matrix), CI workflow,
  docs/phase-1-design.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

llm/capabilities.go

@@ -0,0 +1,45 @@
+package llm
+
+import "slices"
+
+// Capabilities declares what a model (or provider) supports and the limits
+// it imposes. Providers declare defaults; individual models may override.
+// The media pipeline normalizes image inputs against these values before a
+// request is serialized.
+//
+// Zero-value semantics:
+//   - MaxImagesPerReq == 0 means image input is NOT supported.
+//   - MaxImageBytes / MaxImageDimension / ContextWindow == 0 mean
+//     "no declared limit", not zero.
+//   - AllowedImageMIME empty means any MIME type is acceptable
+//     (only meaningful when images are supported at all).
+type Capabilities struct {
+	// MaxImageBytes is the largest single image payload, in bytes.
+	MaxImageBytes int
+	// MaxImageDimension is the largest allowed width or height, in pixels.
+	MaxImageDimension int
+	// AllowedImageMIME lists acceptable image content types
+	// (e.g. "image/jpeg", "image/png").
+	AllowedImageMIME []string
+	// MaxImagesPerReq is the most images one request may carry; 0 = images
+	// unsupported.
+	MaxImagesPerReq int
+
+	SupportsTools      bool
+	SupportsStructured bool
+	SupportsStreaming  bool
+
+	// ContextWindow is the model's context size in tokens, when known.
+	ContextWindow int
+}
+
+// SupportsImages reports whether the target accepts image input.
+func (c Capabilities) SupportsImages() bool { return c.MaxImagesPerReq > 0 }
+
+// MIMEAllowed reports whether the given image MIME type is acceptable.
+func (c Capabilities) MIMEAllowed(mime string) bool {
+	if len(c.AllowedImageMIME) == 0 {
+		return true
+	}
+	return slices.Contains(c.AllowedImageMIME, mime)
+}