Document TAPDB's shipped base object types and why system_user lives in core

[iamh2o]

Problem

• TAPDB explains tables and template packs, but it does not clearly explain the minimal object types it ships as core primitives.
• The repo currently bundles:
  • Generic Object in daylily_tapdb/core_config/generic/generic.json
  • Generic Actor and System User Actor in daylily_tapdb/core_config/actor/actor.json
• system_user exists in core because the repo currently bundles an optional admin/web GUI and auth surface, not because user is a universal domain primitive for every TapDB deployment.

Requested change

• Add a docs pass in README/docs that explicitly explains:
  • most TapDB core entities are generic typed objects seeded from the core template pack
  • the shipped base object layer is intentionally minimal
  • System User Actor is a special bundled actor for TAPDB auth/admin UI support
  • the bundled GUI/admin surface is optional and future extraction/separation is tracked in #12
  • External Object Link is a special case and should be documented separately, not overloaded into the base-object explanation

Acceptance criteria

• README or docs explicitly names the shipped core templates and what role each serves.
• Docs explain that system_user is present because of the bundled GUI/auth path.
• Docs avoid implying that user is a required business-domain primitive for all TapDB consumers.
• The issue references:
  • README.md
  • daylily_tapdb/core_config/generic/generic.json
  • daylily_tapdb/core_config/actor/actor.json
  • daylily_tapdb/user_store.py