Docs: add nav titles across docs (#5689)

docs/reference/api-usage-costs.md

@@ -4,6 +4,7 @@ read_when:
   - You want to understand which features may call paid APIs
   - You need to audit keys, costs, and usage visibility
   - You’re explaining /status or /usage cost reporting
+title: "API Usage and Costs"
 ---
 
 # API usage & costs

docs/reference/device-models.md

@@ -3,6 +3,7 @@ summary: "How OpenClaw vendors Apple device model identifiers for friendly names
 read_when:
   - Updating device model identifier mappings or NOTICE/license files
   - Changing how Instances UI displays device names
+title: "Device Model Database"
 ---
 
 # Device model database (friendly names)

docs/reference/rpc.md

@@ -3,6 +3,7 @@ summary: "RPC adapters for external CLIs (signal-cli, imsg) and gateway patterns
 read_when:
   - Adding or changing external CLI integrations
   - Debugging RPC adapters (signal-cli, imsg)
+title: "RPC Adapters"
 ---
 
 # RPC adapters

docs/reference/session-management-compaction.md

@@ -4,6 +4,7 @@ read_when:
   - You need to debug session ids, transcript JSONL, or sessions.json fields
   - You are changing auto-compaction behavior or adding “pre-compaction” housekeeping
   - You want to implement memory flushes or silent system turns
+title: "Session Management Deep Dive"
 ---
 
 # Session Management & Compaction (Deep Dive)

docs/reference/test.md

@@ -2,6 +2,7 @@
 summary: "How to run tests locally (vitest) and when to use force/coverage modes"
 read_when:
   - Running or fixing tests
+title: "Tests"
 ---
 
 # Tests

docs/reference/transcript-hygiene.md

@@ -4,6 +4,7 @@ read_when:
   - You are debugging provider request rejections tied to transcript shape
   - You are changing transcript sanitization or tool-call repair logic
   - You are investigating tool-call id mismatches across providers
+title: "Transcript Hygiene"
 ---
 
 # Transcript Hygiene (Provider Fixups)