Add efficient local I/O classes

[folker]

What changed

• adds Class 12 on efficient local I/O and safe result publication;
• adds Class 13 on RCC storage architecture, caching, and bottleneck diagnosis;
• adds bounded synthetic-data, direct-I/O, and local-staging shell examples;
• extends both MkDocs and the custom NG renderer with the complete Class 1–13 sequence;
• makes the example scripts downloadable from the custom site;
• updates the course overview, homepage, and learner paths;
• adds regression coverage for class count, navigation, scratch paths, and rendered examples.

Why

Researchers need practical guidance for keeping temporary and random I/O on job-local storage while preserving durable input and final results on approved shared storage. The architecture class explains why metadata, object storage, network links, and caches behave differently under streaming and small-file workloads.

User impact

Learners can compare direct shared-storage access with local staging using synthetic data, use the RCC SLURM_TMPDIR pattern, validate output before publication, and diagnose I/O bottlenecks without exposing infrastructure inventory or patient identifiers.

Integration notes

The supplied v3 patch was malformed and targeted an older navigation layout. This PR repairs the content and adapts it to the current ClusterDocs NG structure, renderer, publication policy, canonical scratch path, and Class 1–13 numbering system.

Validation

• publication lint: PASS
• 41 repository tests: PASS
• 6 protected-app tests: PASS
• custom site build: PASS
• generated-site link checker: PASS
• shell syntax checks: PASS
• git diff --check: PASS

The standalone MkDocs strict build still encounters the branch's existing media/download warnings; it reports no new warnings for Classes 12 or 13.