[#129]:paige:docs, fix nav, content bugs, rewrite stl.md, swap architecture filenames

[steven-varga]

Summary

• mkdocs.yml — fix site_url from steven-varga.ca to vargalabs.github.io/h5cpp; replace flat nav with task-oriented structure (Overview → Getting Started → Architecture), following John's three-persona model
• docs/architecture-types.md ↔ architecture-integration.md — filenames swapped to match content (type system ↔ linalg/STL integration)
• docs/index.md — remove duplicate "With With"
• docs/compiler.md — update stale LLVM 7.0.0 reference to Clang/LLVM 14, 15, 17; fix broken @ref link_h5cpp_install Doxygen link
• docs/architecture-types.md (was architecture-integration.md) — fix NAIVE → NATIVE
• docs/architecture-integration.md (was architecture-types.md) — remove stray editorial note, fix broken [append]: index.mdappend link, strip unpublished TODO
• docs/architecture-parallelism.md — strip stray 4 artifact from code block
• docs/stl.md — full rewrite: dispatch traits (is_contiguous, storage_representation_t), all supported type categories (scalar, STL, linalg, POD struct, custom, raw pointer), std::vector<bool> unsupported note

Test plan

• All nav-wired files confirmed present
• git show --stat HEAD shows renames tracked correctly (99% similarity)
• MkDocs build clean (no broken-link warnings for newly wired pages)
• Verify architecture-types.md now opens to "Type System" content
• Verify architecture-integration.md now opens to "Linear Algebra" content

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