docs(readme): bold mermaid box headings (#11)

Co-authored-by: bxvtr <bxvtr@users.noreply.github.com>

Author: bxvtr

README.md

@@ -128,10 +128,10 @@ Execution, scheduling glue, and Control-Time Event injection when a Control Sche
 
 ```mermaid
 flowchart TB
-    R1["**Runtime**<br/>canonical Event"] --> Entry["**EventStreamEntry**<br/>canonical Event + ProcessingPosition"]
-    Entry --> Core["**TradingChassis Core**<br/>CoreStep / CoreWakeupStep"]
-    Core --> Result["**CoreStepResult**<br/>dispatchable Intents + Control Scheduling Obligation"]
-    Result --> R2["**Runtime**<br/>dispatch / scheduling / I/O"]
+    R1["<b>Runtime</b><br/>canonical Event"] --> Entry["<b>EventStreamEntry</b><br/>canonical Event + ProcessingPosition"]
+    Entry --> Core["<b>TradingChassis Core</b><br/>CoreStep / CoreWakeupStep"]
+    Core --> Result["<b>CoreStepResult</b><br/>dispatchable Intents + Control Scheduling Obligation"]
+    Result --> R2["<b>Runtime</b><br/>dispatch / scheduling / I/O"]
 ```
 
 Core never replaces the Runtime: the Runtime is responsible for feeding canonical
@@ -263,7 +263,7 @@ Control split, dispatchable Intents plus optional Control Scheduling Obligation
 the Runtime, and a boundary that makes parity and testing practical—not a second
 copy of decision logic per environment.
 
-## Public Entrypoints
+### Public Entrypoints
 
 | Entrypoint | Purpose |
 | --- | --- |
@@ -276,7 +276,7 @@ copy of decision logic per environment.
 | `PolicyIntentEvaluator` | Protocol for policy admission (`evaluate_policy_intent`) |
 | Risk Engine (`RiskEngine`) | Convenience `PolicyIntentEvaluator` implementation |
 
-## CoreWakeupStep semantics
+### CoreWakeupStep semantics
 
 CoreWakeupStep is not "parallel Event processing".
 It is deterministic batch processing: the Runtime gives Core an ordered sequence of