ci: remove /ci-all — Pi cannot sustain parallel Docker containers

The Pi runner (3-4 GB RAM, swap heavily loaded) OOMs when /ci-all
triggers test-cgal + quality-gates + doc-build + links simultaneously:
four Docker containers start at once after test-fast completes, each
consuming 150-400 MB, exhausting available RAM.

Fix: /ci-all removed from all three workflow files.  Each keyword
now triggers exactly one job — no parallel container competition.

Safe workflow: one keyword per commit.
  Typical sequence:
    git commit -m 'fix: ... /test-cgal'   → CGAL tests (~5 min)
    git commit -m 'chore: /quality-gates' → style checks (~30 s)

CLAUDE.md: CI table updated with Pi-runner warning note.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -270,6 +270,11 @@ Three jobs in `.gitea/workflows/cpp-tests.yml`:
 | `doc-build` | *(none)* | Doxygen | `/docs` in commit message or `workflow_dispatch` | **active** |
 | `markdown-links` | *(none)* | python3 | `/links` in commit message, weekly cron, `workflow_dispatch` | **active** |
 
+> **⚠ Pi runner limit:** use **one keyword per commit**. The Pi (3-4 GB RAM) cannot run
+> multiple Docker containers simultaneously. `/ci-all` was removed for this reason.
+> Typical workflow: one commit with `/test-cgal`, then if green a separate commit with
+> `/quality-gates`.
+
 Runner: `eulernest` — self-hosted Raspberry Pi, ARM64, Ubuntu 22.04. Docker image: `git.eulernest.eu/conformallab/ci-cpp:latest`. `test-cgal` and `quality-gates` both need `test-fast` to pass first (`needs: test-fast`).
 
 `quality-gates` runs four required structural gates: `license-headers.sh`, `cgal-conventions.py`, `codespell.sh`, `shellcheck.sh --strict`.  Seven more gates (clang-format, cmake-format, cppcheck, sanitizers, clang-tidy, multi-compiler, reproducible-build) are local-only — see `scripts/quality/README.md`.