fix(install): enable memory toolset so clean Hermes installs expose Retinue

fix(install): enable memory toolset so clean Hermes installs expose Retinue

Found on a fresh Hermes "Blank Slate" install (valeriapc, 2026-08-30):
Retinue installed and selected via memory.provider, hermes memory status
reported the plugin available — yet the session had no retinue_memory_*
tools and no Retinue system-prompt block. Blank Slate setup writes
platform_toolsets.cli = [file, skills, terminal, vision] and lists memory
in agent.disabled_toolsets; with that gate closed Hermes initializes the
provider but withholds its entire model-facing surface.

- Install Retinue now runs `hermes tools enable --platform cli memory`
  after setting memory.provider. Verified in Hermes source
  (tools_config.py _save_platform_tools) that this both adds the toolset
  to platform_toolsets.cli and removes it from agent.disabled_toolsets.
- Failure of that step is non-fatal but fully visible: captured output
  and the manual command are printed (no silent 2>/dev/null), plus a note
  that other platforms (telegram, discord, ...) each need their own
  --platform <name> enable.
- Docs: Documentation/index.org (five installer steps),
  Documentation/Development/index.org (full step list incl. the
  pip -> ensurepip -> uv dependency chain), AGENTS.org (deploy section +
  new Blank Slate memory-toolset pitfall).

Verified with a stubbed-environment ad-hoc harness (10/10): the stub
hermes CLI receives `tools enable --platform cli memory`; a CLI that
rejects it produces a warning with the captured error and manual command
while the install still completes. Live fix applied on valeriapc:
memory now in platform_toolsets.cli and gone from agent.disabled_toolsets.