Pi: planning skills should check/update the project's llmwiki

[jinyeow]

Problem

When a project has an llmwiki (Karpathy's raw-sources/wiki/schema pattern, e.g. E:/HollardInsuranceRetail/wiki), planning-phase work (grill-with-docs, to-spec, and similar) doesn't check it for existing notes, and doesn't write new durable facts back into it. Facts like "FDM and SDS NSG rules live under DPC/ in T2-Infrastructure" get rediscovered instead of reused, because nothing in the planning chain looks at or updates the wiki.

Desired behavior

• When planning work starts in a project directory that has an llmwiki, the relevant planning skill(s) check the wiki for notes relevant to the task before/while grilling or drafting a spec.
• When planning surfaces a durable fact worth keeping (an infra layout quirk, a "where does X live" answer, a gotcha), the skill records it into the wiki rather than letting it live only in the spec or conversation.
• Detection of "this project has an llmwiki" should be generic (e.g. a wiki/ dir with the expected schema), not hardcoded to one project.

Scope

Pi side: likely touches grill-with-docs, to-spec, and/or a shared planning-support module under ai-agents/skills/ (portable), plus whatever Pi-specific wiring (pi/skills/, pi/extensions/) is needed to invoke it during planning. Check whether llmwiki-insights skill's read logic can be reused rather than duplicated.

Out of scope

• The wiki's own lint/contradiction-check operation (that's the wiki's own AGENTS.md).
• Claude Code's equivalent — tracked separately (see linked issue).