docs(diagrams): add template and decompose CRITICAL diagrams [ADR-040]

[SatoryKono]

Motivation

• Reduce layout overload and Dagre failures by decomposing oversized architecture diagrams into focused, renderable Views and standardize metadata for CI and onboarding.
• Provide a single canonical template and a formal superseded marker so historical originals are retained but excluded from automated renders.
• Ensure consistent theming and subgraph styling by pointing authors to the external theme and forbidding inline %%{init:} blocks for new files.

Description

• Added docs/02-architecture/mmd-diagrams/_template.mmd with standardized metadata fields (@status, @view, @parent, @nodes) and theming guidance (no %%{init:} for new files).
• Updated all architecture/*.mmd files to include normalized header metadata (%% @status active and %% @nodes <n>) and recomputed node counts for accuracy.
• Decomposed CRITICAL diagrams into focused Views by creating new files (examples: architecture/01a-01c-*, architecture/13a-13d-*, foundation/01a-01c-*, foundation/50a-50c-*) and added %% @view/%% @parent metadata to each decomposed file.
• Marked original heavy diagrams with a standardized SUPERSEDED header (%% @status superseded + %% @superseded-by ...) and updated docs/02-architecture/mmd-diagrams/README.md to link ADR-040, list decomposed views, annotate superseded files, and provide a recommended onboarding order.
• Updated docs/02-architecture/mmd-diagrams/render.sh to skip files containing @status superseded so CI rendering excludes historical originals.

Testing

• Ran node-count verification (grep-based heuristic) across decomposed files and confirmed @nodes matches the computed unique node counts and all decomposed views are ≤20 nodes (check succeeded).
• Performed shell syntax check (bash -n docs/02-architecture/mmd-diagrams/render.sh) and Python compile check for the lint script (python -m compileall scripts/lint_diagrams.py), both of which succeeded.
• Executed python scripts/lint_diagrams.py which ran (reported "All diagrams pass policy checks" in this environment), noting it reported zero files processed due to environment scope but the script exercised the updated code path.
• Attempted a render smoke-test with mmdc but it failed because the mmdc binary is not installed in the execution environment; pre-commit hooks run in this environment also surfaced unrelated repository-wide checks (auto-formatting, missing pip-audit, and root-level VCR cassette placement) which are external to these diagram edits.

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[SatoryKono]

Superseded by #2422.