Harmonize feature install scripts and metadata across src/

[Copilot]

This PR tightens repository-wide feature consistency and removes a few script-level deviations from the conventions already used in src/. The main focus is making feature installation behavior more coherent and reducing avoidable shell fragility.

• Install script coherence

  • Standardizes feature install scripts around small main()-driven entrypoints and explicit helper functions.
  • Replaces ad-hoc cp/mv flows with install-based file placement for clearer permissions and more predictable behavior.
  • Adds an explicit source-binary check in the Hermes feature before installation.

• Shell robustness

  • Removes the dynamic eval lookup from the Rust lifecycle hook and replaces it with explicit handling for supported environment variables.
  • Makes the Rust post-create flow explicit about whether follow-up rustup adjustments should run after directory setup.

• Feature metadata alignment

  • Renames the Hermes feature to match the naming style used by the other features.
  • Tightens the Hermes description so it reads like the rest of the catalog.
  • Updates the generated-facing Hermes README header/summary to stay aligned with the feature metadata.

• VS Code cache script cleanup

  • Drops the broad ShellCheck suppression by normalizing _REMOTE_USER_HOME handling.
  • Replaces loop-string parsing with explicit per-channel setup for the stable and insiders cache directories.

install -D -m 0755 "${TOOL_SOURCE}" "${TOOL_TARGET}"

That pattern now replaces less structured copy/move logic in feature installers, making installation intent and file mode handling consistent across features.