feat: sync rules across all harnesses + agents to opencode/kilo

Add Rule as a first-class canonical kind (rules/<name>.md, loaded like
agents) and propagate it the way each harness actually loads it:

- claude-code: native ~/.claude/rules directory symlink (preserves rule
  path-scoping frontmatter); rules NOT folded into CLAUDE.md.
- opencode/kilo/zed/crush: fold rule bodies into the global AGENTS.md
  always-on instructions file (frontmatter stripped). crush has no global
  instructions file, so register the absolute AGENTS.md path in
  options.context_paths (defaults are re-prepended at load, so nothing is
  clobbered).
- goose: fold into ~/.config/goose/.goosehints.
- cagent: fold into the per-agent instruction.

Also:
- Wire markdown agents to opencode (~/.config/opencode/agents) and fix the
  kilo agents symlink: plural ~/.config/kilo/agents (singular "agent" is a
  silent no-op on current Kilo CLI).
- Add ManagesAgents/ManagesRules to HarnessCapabilities + ImportResult.Rules;
  claude-code/opencode import rules/agents round-trip.
- Centralize instruction selection in Bundle.InstructionText /
  InstructionTextWithRules (replaces per-adapter override duplication).
- init scaffolds + imports rules; README capability matrix gains
  Agents/Rules columns with native-vs-folded footnotes.

Grounded each harness's sink against official docs + config source this
session. Gate: gofmt, go vet, go test -race ./..., golangci-lint (0),
govulncheck (clean).

internal/cli/init.go

@@ -93,6 +93,7 @@ func runImport(cmd *cobra.Command, reg *adapter.Registry, root, home string, pic
 	}
 	seenSkills := map[string]bool{}
 	seenAgents := map[string]bool{}
+	seenRules := map[string]bool{}
 	seenMCP := map[string]bool{}
 	var instructions []string
 
@@ -121,6 +122,14 @@ func runImport(cmd *cobra.Command, reg *adapter.Registry, root, home string, pic
 			seenAgents[key] = true
 			bundle.Agents = append(bundle.Agents, a)
 		}
+		for _, r := range res.Rules {
+			key := r.Name + "|" + r.Body
+			if seenRules[key] {
+				continue
+			}
+			seenRules[key] = true
+			bundle.Rules = append(bundle.Rules, r)
+		}
 		for _, m := range res.MCP {
 			if seenMCP[m.Name] {
 				continue
@@ -153,8 +162,8 @@ func runImport(cmd *cobra.Command, reg *adapter.Registry, root, home string, pic
 		return err
 	}
 	_, _ = fmt.Fprintf(cmd.OutOrStdout(),
-		"imported from %v into %s\n  skills:       %d\n  agents:       %d\n  mcp servers:  %d\n  instructions: %d source(s)\n",
-		picked, root, len(bundle.Skills), len(bundle.Agents), len(bundle.MCP.Servers), len(instructions),
+		"imported from %v into %s\n  skills:       %d\n  agents:       %d\n  rules:        %d\n  mcp servers:  %d\n  instructions: %d source(s)\n",
+		picked, root, len(bundle.Skills), len(bundle.Agents), len(bundle.Rules), len(bundle.MCP.Servers), len(instructions),
 	)
 	return nil
 }
@@ -172,7 +181,7 @@ const importedProfileBody = "# harness-sync profile \xe2\x80\x94 generated by in
 	"models: []\n"
 
 func writeCanonical(root string, b *canonical.Bundle, picked []string) error {
-	for _, sub := range []string{"profiles", "skills", "agents", "instructions"} {
+	for _, sub := range []string{"profiles", "skills", "agents", "rules", "instructions"} {
 		if err := os.MkdirAll(filepath.Join(root, sub), 0o750); err != nil {
 			return err
 		}
@@ -233,6 +242,19 @@ func writeCanonical(root string, b *canonical.Bundle, picked []string) error {
 			return err
 		}
 	}
+	for _, r := range b.Rules {
+		rel := r.Path
+		if rel == "" {
+			rel = safeFilename(r.Name) + ".md"
+		}
+		path := filepath.Join(root, "rules", rel)
+		if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
+			return err
+		}
+		if err := os.WriteFile(path, []byte(r.Body), 0o600); err != nil {
+			return err
+		}
+	}
 	if b.Instructions.Global != "" {
 		if err := os.WriteFile(filepath.Join(root, "instructions", "global.md"),
 			[]byte(b.Instructions.Global), 0o600); err != nil {