docs: convert standard diagrams from draw.io PNGs to inline Mermaid

Gitea renders mermaid inline, so the flow/state/hierarchy/DAG diagrams
move to text-in-markdown: auto-layout (removes the manual overlap-prone
draw.io step), diffable source, no committed binaries, and a dark-text
theme so labels stay legible. Keep draw.io PNGs only for the two complex
bespoke diagrams (logical architecture, env2 topology) where pixel
control still wins. All 24 mermaid blocks validated by rendering.

docs/requirements/Component-InboundAPI.md

@@ -123,8 +123,41 @@ API method scripts are compiled at central startup — all method definitions ar
 
 ## Request Flow
 
-![inboundapi-request-flow](diagrams/inboundapi-request-flow.png)
-<!-- source: diagrams/inboundapi-request-flow.drawio — edit, then re-export with export-drawio.sh -->
+```mermaid
+%%{init: {'theme':'base', 'themeVariables': {'textColor':'#111111','lineColor':'#555555','edgeLabelBackground':'#ffffff','fontSize':'15px'}}}%%
+flowchart TD
+    ext(["External System"])
+    api["Inbound API (Central)"]
+    s1["1. Extract API key from request"]
+    s2["2. Validate key exists and is enabled"]
+    s3["3. Resolve method by name"]
+    s4["4. Check API key is in method's approved list"]
+    s5["5. Validate and deserialize parameters"]
+    s6["6. Execute implementation script<br/>(subject to method timeout)"]
+    s7["7. Serialize return value"]
+    s8["8. Return response"]
+
+    ext --> api
+    api --> s1
+    s1 --> s2
+    s2 --> s3
+    s3 --> s4
+    s4 --> s5
+    s5 --> s6
+    s6 --> s7
+    s7 --> s8
+
+    classDef start fill:#d5e8d4,stroke:#82b366,color:#111111;
+    classDef proc fill:#dae8fc,stroke:#6c8ebf,color:#111111;
+    classDef dec fill:#fff2cc,stroke:#d6b656,color:#111111;
+    classDef warn fill:#ffe6cc,stroke:#d79b00,color:#111111;
+    classDef alt fill:#e1d5e7,stroke:#9673a6,color:#111111;
+    class ext start
+    class api proc
+    class s1,s2,s3,s4,s5,s7 dec
+    class s6 alt
+    class s8 warn
+```
 
 ## Implementation Script Capabilities