🌐 Add cross-repo index system (Tier 1)

.blackroad/README.md

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+# .blackroad/ - Cross-Repo Index System
+
+This directory contains the **Tier 1 local index** for this repository.
+
+## Files
+
+- **workflow-index.jsonl** - Append-only log of all workflows in this repo
+- **workflow-index-schema.json** - JSON schema for validation
+- **last-sync.txt** - Last sync timestamp
+
+## How It Works
+
+1. When an issue is created/updated with a workflow ID label
+2. `workflow-index-sync.yml` runs automatically
+3. Extracts metadata (state, scope, risk, dependencies, etc.)
+4. Appends to `workflow-index.jsonl`
+5. Commits the update
+
+## Querying
+
+```bash
+# Find all Active workflows
+jq 'select(.state=="Active")' .blackroad/workflow-index.jsonl
+
+# Find workflows with dependencies
+jq 'select(.deps | length > 0)' .blackroad/workflow-index.jsonl
+
+# Find System-scope workflows
+jq 'select(.scope=="System")' .blackroad/workflow-index.jsonl
+
+# Find Red traffic light workflows
+jq 'select(.traffic_light=="🔴")' .blackroad/workflow-index.jsonl
+```
+
+## Cross-Repo Dependencies
+
+Format: `{owner}/{repo}#{WORKFLOW_ID}`
+
+Example:
+```json
+{
+  "id": "WF-20260213-SVC-0005",
+  "deps": [
+    "WF-20260212-SYS-0001",                    // Local dependency
+    "BlackRoad-OS/api#SEC-20260213-PUB-0006"  // Cross-repo dependency
+  ]
+}
+```
+
+## Architecture
+
+This is **Tier 1** (Local Index) of a 3-tier system:
+
+- **Tier 1**: Local repo index (this file)
+- **Tier 2**: Organization-wide GitHub Project
+- **Tier 3**: Global discovery API (optional)
+
+See: ~/CROSS_REPO_INDEX_STRATEGY.md
+
+## Maintenance
+
+- Index is **append-only** (never delete entries)
+- Updates replace old entries by ID
+- No manual editing required
+- Scales to millions of workflows