docs: fix volume-content mermaid diagram rendering

[forrestIsRunning]

Problem

The Volume content sequence diagram in docs/ARCHITECTURE.md does not render on GitHub:

Parse error on line 12:
... for BYOC teams;<br/>SDK stores it and f
-----------------------^

Mermaid sequence diagrams treat ; as a statement separator (equivalent to a newline). After BYOC teams;, the parser starts a new statement at <br/> and fails. The same diagram also uses HTML < / > for domain placeholders; those are invalid tokens in current Mermaid.

This is a docs-only bug. CONTRIBUTING.md says documentation fixes can skip the issue-first step.

Fix

Use Mermaid entity codes in that sequence diagram, which is the documented way to keep the original text:

character	in source
;	#59;
<	#lt;
>	#gt;

The rendered note and api.<domain> placeholders stay the same. Surrounding prose is unchanged.

Diagram after the change (should render below)

sequenceDiagram
    autonumber
    participant U as SDK
    participant API as API
    participant PG as PostgreSQL
    participant VC as volume-content API (belt)

    U->>API: POST /volumes (create) or GET /volumes/{id}
    API->>PG: persist / load volume row
    API->>API: mint JWT (aud = https://api.#lt;domain#gt;)<br/>resolve domain
    API-->>U: { volumeID, name, token, domain? }
    Note over U: domain is returned only for BYOC teams#59;<br/>SDK stores it and falls back to api.#lt;E2B_DOMAIN#gt; otherwise
    U->>VC: /volumecontent/{id}/... at api.#lt;domain#gt;<br/>Authorization: Bearer token
    VC->>VC: verify token (audience must match its own origin)
    VC-->>U: file content

Loading

Validation

• Reproduced the GitHub parse error against current main
• Parsed all six diagrams in docs/ARCHITECTURE.md with Mermaid 11.12.0 after the change
• Docs-only; make test / make lint do not apply

Related: #3621 also addresses the GitHub parse error by escaping the semicolon. This change also replaces the HTML entities so the diagram parses in current Mermaid, not only GitHub's renderer.

[HeyiSun]

duplicate with #3621