Include order is owned by clang-format

C++ include order is owned by clang-format: the tangled .clang-format (generated from doc/knowledge/architecture/clang_format_config.org) is the single source of truth. Never hand-tune include order in source files, and reject review suggestions that ask for it. If an ordering suggestion sounds sensible, the change is made at the clang-format level — edit the literate org config, retangle, and let the formatter apply it everywhere.

Why: Marco, 2026-06-05, while triaging Gemini review comments on PR #1070 that suggested same-target includes before external-component includes: "in terms of includes order, remember we go via clang format… any changes must be done at the clang format level, if they sound sensible." Manual deviations are reverted by the next format run or the nightly format bot. Precedent: the Windows SDK ordering constraint (iphlpapi.h after windows.h) was encoded as an IncludeCategories entry rather than per-file pragmas.

How to apply: When a review comment, lint suggestion, or instinct says to reorder #include lines: do not edit the source file ordering by hand. Either reject (if it fights the alphabetical-within-category policy) or, if the rule is genuinely sensible, add it to the IncludeCategories in clang_format_config.org, run the tangle_clang_format target, and reformat. Always run clang-format -i on touched files so order matches the config.