docs: author the C coding standard for reference/c-standard

[coretl]

Target page

reference/c-standard

No source exists — this is new content identified in Interview1 §4 as needed
for server contributors.

Category: author-from-scratch

What a human must do (~4 hours)

Write the C coding standard for PandABlocks server contributors, covering at
minimum:

1. **Naming conventions** — functions, variables, macros, types (typedef'd
   structs, enums).
2. **File structure** — header guard style, include order, extern "C" guards.
3. **Error handling** — return-code conventions, errno usage, logging macros.
4. **Memory management** — ownership rules, allocation patterns, common pitfalls
   in the server's context.
5. **Comment style** — what warrants a comment; doxygen vs plain C comments.
6. **Formatting** — indentation (tabs/spaces), brace placement, line length.
7. **Project-specific idioms** — any server-specific patterns (e.g. lock/unlock
   wrappers, the config vs data thread boundary).

Post as a PR against docs/reference/c-standard.md on the docs branch.