Installers: verify the memory/RAG stack at install time + auto-install native prerequisites

[jdmanring]

Summary

The one-command installers (setup.sh, setup.ps1) install requirements.txt
(which includes chromadb + fastembed, the semantic-memory / RAG stack) but never
verified that stack actually loads. fastembed pulls in onnxruntime, whose
native runtime has platform prerequisites pip cannot provide — so a silent
failure demotes semantic memory to keyword search unnoticed. (This bit Windows:
the Microsoft VC++ Redistributable was missing, so onnxruntime's DLL failed to
load and memory silently degraded.)

Change

• tooling/verify_memory_stack.py: imports chromadb + fastembed and, on failure,
  prints a platform-specific fix (Windows -> VC++ redist; FreeBSD -> Rust build;
  else -> pip). Exit 0 healthy / 1 degraded.
• setup.ps1: auto-installs the Microsoft VC++ Redistributable (the native
  prerequisite for onnxruntime), then runs the verifier.
• setup.sh: runs the verifier after install, warns (non-fatal) with the fix.

Base branched from develop because these installer files exist only there (they
are staged fork contributions not yet upstreamed); this is upstream-candidate.

Note: build-freebsd-app.sh carries the same check on feat/qt-native-freebsd-app.