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/adapters/zed/import.go

@@ -0,0 +1,19 @@
+package zed
+
+import (
+	"path/filepath"
+
+	"github.com/lukaszraczylo/harness-sync/internal/adapter"
+	"github.com/lukaszraczylo/harness-sync/internal/adapter/common"
+)
+
+func importFrom(home string) (*adapter.ImportResult, error) {
+	cfgPath := filepath.Join(home, ".config", "zed", "settings.json")
+	// context_servers entries use source:"custom" for stdio; the MCP command
+	// field maps directly to canonical MCPServer.Command.
+	servers, err := common.ImportMCPFromJSONFile(cfgPath, "context_servers")
+	if err != nil {
+		return nil, err
+	}
+	return &adapter.ImportResult{MCP: servers}, nil
+}