step 5 (complete): docs purge, fresh ARCHITECTURE + ROADMAP + CHANGELOG

Purged 29,966 lines of stale chat-switchboard documentation:
  - 41 docs/ files (ICD specs, design docs, archive, workflow docs)
  - 5 root MD files (CHANGESET, TURNOVER, ICD-DRIFT-AUDIT, etc.)

New documentation:
  - docs/ARCHITECTURE.md — kernel components, design principles, data layer
  - ROADMAP.md — v0.1.0 through v0.5.0 MVP with decision log
  - CHANGELOG.md — fresh, starting from v0.1.0 fork
  - README.md — rewritten for switchboard-core

Also in this commit:
  - config.go: stripped 7 dropped fields, DB default → switchboard_core
  - pages/loaders.go: stripped provider/model/notes/projects loaders
  - pages/pages.go: stripped persona store lookup
  - handlers/workflows.go: stripped persona tool grants
  - main.go: stripped team provider routes, avatar routes

Production code: zero references to deleted packages, stores, or models.
-29,966/+352 lines across 73 files.

server/handlers/workflows.go

@@ -293,10 +293,6 @@ func (h *WorkflowHandler) Publish(c *gin.Context) {
 	snapshotStages := make([]stageSnapshot, len(stages))
 	for i, st := range stages {
 		snapshotStages[i] = stageSnapshot{WorkflowStage: st}
-		if st.PersonaID != nil && h.stores.Personas != nil {
-			grants, _ := h.stores.Personas.GetToolGrants(c.Request.Context(), *st.PersonaID)
-			snapshotStages[i].ToolGrants = grants
-		}
 	}
 
 	snapshot := map[string]interface{}{