feat(brain): add path field to brain_ingest for /ingest-path routing

Adds an optional path field to brain_ingest so Claude can ingest files
or directories directly by path without embedding content in the call.
Routing: path set → /ingest-path; content+source set → /ingest; neither → error.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/skills/brain/skill.go

@@ -58,9 +58,10 @@ func (s *Skill) Tools() []registry.ToolDef {
 		tools = append(tools, registry.ToolDef{
 			Name:        "brain_ingest",
 			Description: "Ingest text content into the brain wiki (brain/wiki/). Calls an LLM to produce structured wiki pages. Use for substantial documents, articles, or knowledge worth structuring. Returns the list of wiki pages written.",
-			InputSchema: schema([]string{"content", "source"}, map[string]any{
+			InputSchema: schema([]string{}, map[string]any{
 				"content": str,
 				"source":  map[string]any{"type": "string", "description": "human-readable name for the content, e.g. 'article-on-raft.md'"},
+				"path":    map[string]any{"type": "string", "description": "absolute path to a file or directory to ingest; if set, content and source are not needed"},
 				"dry_run": map[string]any{"type": "boolean"},
 			}),
 		})