docs: restructure architecture documentation

[reiase]

Summary

• Consolidate fragmented and legacy architecture pages into a smaller set of bilingual, status-aware design documents.
• Add dedicated activation/injection and distributed profiler design pages, together with architecture and profiler SVG diagrams.
• Reorganize the MkDocs navigation and update references across guides, examples, CLI documentation, tests, and contributor guidance.
• Keep the TorchProbe overhead invariants in the main overhead design document and update the corresponding regression guard.
• Move the local documentation preview to 127.0.0.1:8001 and invoke MkDocs through the selected Python interpreter.

Why

The architecture documentation had accumulated overlapping pages, duplicated explanations, and stale cross-references. This refactor establishes clearer ownership, reading order, and current-versus-target design status while retaining the relevant technical contracts in consolidated pages.

Impact

This changes documentation structure and developer guidance only; it does not change runtime APIs, SQL table schemas, or collector behavior. Existing links to retired design pages are updated to their new canonical locations.

Validation

• git diff --check
• uv run --isolated --with-requirements docs/requirements.txt python -m mkdocs build --strict
• PROBING=0 ./.venv/bin/pytest tests/regression/profiling/test_overhead_invariants.py -q (5 passed)
• Verified that retired design-page paths have no remaining tracked references.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
...s/regression/profiling/test_overhead_invariants.py	100.00% <100.00%> (ø)

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