PlotPickle Agents: default compute plus per-agent overrides

[BryanHarrisScripts]

Goal

Give PlotPickle's own story/product Agents one clear configuration surface that assigns compute supplied by Local Story Mode and Cloud Story Mode.

Product decision

This is PlotPickle Agent configuration, not BUZZ configuration.

Local Story Mode and Cloud Story Mode define available compute/resources. The Agents surface chooses a default resource/model and permits a bounded override for an individual PlotPickle Agent.

BUZZ is explicitly outside this issue. BUZZ may host/community-connect agents elsewhere, but it is not the source of truth for PlotPickle Agent provider/model assignment.

Required behavior

1. Provide one PlotPickle Agent default assignment used when an Agent has no explicit override.
2. Allow a per-Agent override for provider/model/capability where the selected resource actually supports the Agent task.
3. Make inheritance obvious: Default versus Override.
4. If an override becomes unavailable, fail truthfully and expose the condition; do not silently jump to a paid cloud provider.
5. Local and cloud choices must come from the existing provider/routing capability model, not a duplicate hard-coded runtime catalog.
6. Preserve Agent authority boundaries: compute assignment cannot expand tools, canon authority, repository authority or Human approval rights.
7. Keep BUZZ keys, room membership, presence and BUZZ runtime settings out of this surface.
8. Keep configuration compatible with future additional skins: behavior/state is product-owned; Skin V1 is presentation.

Acceptance criteria

• A visible PlotPickle Agents surface shows the global default compute assignment.
• Individual PlotPickle Agents can inherit the default or select an explicit supported override.
• Unsupported provider/model combinations cannot be selected.
• Missing/unavailable overrides do not silently fall back to paid compute.
• BUZZ configuration is not read or written by this surface.
• Existing Human/canon/tool authority is unchanged.
• Focused tests cover default inheritance, override presentation and the no-BUZZ/no-silent-fallback boundary.
• Production build and required GitHub CI are green.

Do not change

Agent creative authority, PPF/canon rules, BUZZ identity/community configuration, provider credential storage, or unrelated Agent orchestration.