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/adapters/kilo/kilo.go

@@ -38,7 +38,9 @@ func (a *Adapter) Capabilities() adapter.HarnessCapabilities {
 		ManagesModels:       true,
 		ManagesMCP:          true,
 		ManagesSkills:       true,
-		ManagesInstructions: false,
+		ManagesAgents:       true,
+		ManagesRules:        true,
+		ManagesInstructions: true,
 		HasBuiltInSub:       false,
 	}
 }
@@ -58,8 +60,11 @@ func (a *Adapter) Render(b *canonical.Bundle) (*adapter.FileSet, error) {
 	fs := adapter.NewFileSet()
 	base := filepath.Join(a.Home, ".config", "kilo")
 
+	// Kilo CLI reads global markdown subagents from ~/.config/kilo/agents/<name>.md
+	// (PLURAL — the singular "agent/" used by older OpenCode-fork builds is a
+	// silent no-op on current Kilo).
 	fs.Add(adapter.File{
-		Dest:          filepath.Join(base, "agent"),
+		Dest:          filepath.Join(base, "agents"),
 		Kind:          adapter.SymlinkDir,
 		SymlinkTarget: filepath.Join(b.Root, "agents"),
 	})
@@ -69,6 +74,13 @@ func (a *Adapter) Render(b *canonical.Bundle) (*adapter.FileSet, error) {
 		Kind:          adapter.SymlinkDir,
 		SymlinkTarget: filepath.Join(b.Root, "skills"),
 	})
+	// kilo has no global rules directory; ~/.config/kilo/AGENTS.md is the
+	// always-on global instructions file, so fold rules into it.
+	fs.Add(adapter.File{
+		Dest:    filepath.Join(base, "AGENTS.md"),
+		Kind:    adapter.RenderedFile,
+		Content: []byte(b.InstructionTextWithRules(name)),
+	})
 
 	cfgPath := filepath.Join(base, "kilo.json")
 	existing, err := common.ReadExistingFile(cfgPath)