[enhancement] ORPHAN_CONCEPT signal — distinct display channel in sandman_handoff.md

Context

PR #10084 (resolves #10035) detects orphan concepts (CONCEPT nodes with no IMPLEMENTED_BY edge — concepts that exist in the ontology but aren't anchored to any source code) and emits them as logger.warn during ingestion. The choice to suppress them from the capability-gap channel was deliberate: orphans are ontology data-quality signals, not coverage gaps, and conflating them would dilute the signal GoldenPathSynthesizer consumes for sandman_handoff.md.

As the ontology grows (#10050 description enrichment, #10036 Memory Core concept discovery, #10037 ChromaDB embedding), orphans may become frequent enough that invisibility becomes the wrong default. A dedicated display channel is the right fix — keeps the main gap channel clean while making orphans actionable for curators.

The Fix

1. ConceptIngestor emits [ORPHAN_CONCEPT] entries to a new property channel (e.g., node.properties.dataQualityFlag to keep it separate from capabilityGap) OR to the same capabilityGap JSON array with the distinct tag — decide during implementation based on which is cleaner downstream
2. GoldenPathSynthesizer categorizes [ORPHAN_CONCEPT] into a new array parallel to testGaps / guideGaps / exampleGaps
3. New rendering section in sandman_handoff.md: ### ⚠️ Orphaned Concepts (X of Y items) with the same 5-item limit pattern
4. TTL pruning applies uniformly

Decision Needed During Implementation

Should ORPHAN_CONCEPT share the capabilityGap property channel with TEST_GAP/GUIDE_GAP/EXAMPLE_GAP, or live on its own property? Sharing reduces GoldenPathSynthesizer's node-scanning work (one loop not two); separating keeps the "coverage gap" semantics pure. Lean: share the channel, since the tag-prefix categorization pattern already handles taxonomy separation downstream.

Acceptance Criteria

• ConceptIngestor attaches [ORPHAN_CONCEPT] entries to orphan nodes
• GoldenPathSynthesizer categorizes the new tag + renders dedicated section
• logger.warn simplified — warn only on first detection per orphan (TTL-based dedup) or removed entirely if graph persistence is enough signal
• Existing tests still pass
• New test: ingesting an orphan concept causes ⚠️ Orphaned Concepts section to appear in handoff

Origin Session ID

62d6f155-e57f-4279-9b59-36c9e4ecbc5e — flagged as out-of-scope in PR #10084 body

Related

• Parent epic: #10030
• Origin PR: #10084