fix(adapters): ground native schemas, merge-not-replace, add goose/cagent/zed

- common/mcp.go: MCPStyle enum + BuildMCPMapStyled for claude/crush/opencode/zed dialects
- common/jsonmerge.go: MergeJSONKeys (JSON-first, JSONC fallback) preserves user keys;
  fix: try plain json.Unmarshal before StripJSONComments to avoid mangling URLs with //
- common/yamlmerge.go: MergeYAMLKeys for YAML configs (goose)
- common/blocks.go: add ProvidersAsMap for opencode map-shaped provider key
- claudecode: merge settings.json (preserves hooks/permissions/env); MCPClaudeStyle (no type field)
- crush: fix mcp key (was mcpServers); MCPCrushStyle entries include type field; merge crush.json; fix import key mcp
- kilo: drop providers key (kilo has none); MCPOpencodeStyle (local/remote); merge kilo.json
- opencode: fix provider (singular map) + model (not default_model); MCPOpencodeStyle; merge jsonc; fix import key mcp
- goose: new adapter — YAML merge, extensions map, splitProviderModel, import reconstructs MCP from extensions
- cagent: new adapter — renders starter default.yaml, import returns empty
- zed: new adapter — merge settings.json, context_servers (MCPZedStyle) + agent.default_model
- docs: append Grounded harness schemas section to design spec

internal/adapter/common/mcp.go

@@ -0,0 +1,102 @@
+package common
+
+import "github.com/lukaszraczylo/harness-sync/internal/canonical"
+
+// MCPStyle selects the dialect for MCP server entries.
+type MCPStyle int
+
+const (
+	// MCPClaudeStyle: claude-code shape — {command, args, env, url, transport}.
+	MCPClaudeStyle MCPStyle = iota
+	// MCPCrushStyle: crush shape — adds type: stdio|http|sse.
+	MCPCrushStyle
+	// MCPOpencodeStyle: kilo + opencode shape — type: local|remote, command as []string.
+	MCPOpencodeStyle
+	// MCPZedStyle: zed context_servers — {enabled, source, command, args} or {enabled, url}.
+	MCPZedStyle
+)
+
+// BuildMCPMapStyled returns the MCP map for the given harness dialect.
+func BuildMCPMapStyled(reg *canonical.MCPRegistry, style MCPStyle) map[string]any {
+	out := map[string]any{}
+	if reg == nil {
+		return out
+	}
+	for _, s := range reg.Servers {
+		out[s.Name] = mcpEntry(s, style)
+	}
+	return out
+}
+
+func mcpEntry(s canonical.MCPServer, style MCPStyle) map[string]any {
+	e := map[string]any{}
+	switch style {
+	case MCPClaudeStyle:
+		if s.Command != "" {
+			e["command"] = s.Command
+		}
+		if len(s.Args) > 0 {
+			e["args"] = s.Args
+		}
+		if s.URL != "" {
+			e["url"] = s.URL
+		}
+		if s.Transport != "" {
+			e["transport"] = s.Transport
+		}
+		if len(s.Env) > 0 {
+			e["env"] = s.Env
+		}
+	case MCPCrushStyle:
+		if s.URL != "" {
+			t := s.Transport
+			if t == "" {
+				t = "http"
+			}
+			e["type"] = t
+			e["url"] = s.URL
+		} else {
+			e["type"] = "stdio"
+			if s.Command != "" {
+				e["command"] = s.Command
+			}
+			if len(s.Args) > 0 {
+				e["args"] = s.Args
+			}
+			if len(s.Env) > 0 {
+				e["env"] = s.Env
+			}
+		}
+	case MCPOpencodeStyle:
+		if s.URL != "" {
+			e["type"] = "remote"
+			e["url"] = s.URL
+		} else {
+			e["type"] = "local"
+			cmd := []string{}
+			if s.Command != "" {
+				cmd = append(cmd, s.Command)
+			}
+			cmd = append(cmd, s.Args...)
+			e["command"] = cmd
+			if len(s.Env) > 0 {
+				e["environment"] = s.Env
+			}
+		}
+		e["enabled"] = true
+	case MCPZedStyle:
+		e["enabled"] = true
+		if s.URL != "" {
+			e["url"] = s.URL
+		} else {
+			e["source"] = "custom"
+			if s.Command != "" {
+				e["command"] = s.Command
+			}
+			if len(s.Args) > 0 {
+				e["args"] = s.Args
+			}
+		}
+	}
+	return e
+}