feat(import): user-extensible BOR_IMPORT_EXTENSIONS — any well-formed extension, A9 family stays the default

.env.example

@@ -40,8 +40,13 @@ BOR_RRF_K=60                      # Reciprocal Rank Fusion damping constant
 # --- Agent document tools (phase 37: grounded turns may list + read) ---
 # BOR_AGENT_MAX_ROUNDS=10        # hard cap on agent tool rounds per turn (0 = no tools)
 
-# --- Import scope (A9 formats; may only narrow, never widen) ---
-# BOR_IMPORT_EXTENSIONS=md,markdown,txt,yaml,yml,json,py,container,network,volume,image,pod,kube,swap,os,endpoint,j2
+# --- Import scope (A9 default; ANY well-formed extension is allowed) ---
+# Comma-separated file extensions (lowercase, no dot) the importer reads.
+# Any extension is allowed — the value below is the built-in default (the
+# A9 family: the original seven + the quadlet family + jinja ``j2``); add
+# your own (e.g. md,sh,toml) or narrow it (e.g. md). A blank list or a
+# malformed token (e.g. md,sh!) fails startup loudly, naming the value.
+BOR_IMPORT_EXTENSIONS=md,markdown,txt,yaml,yml,json,py,container,network,volume,image,pod,kube,swap,os,endpoint,j2
 # BOR_SUGGESTIONS=["How is my Kubernetes cluster set up?"]   # JSON list of onboarding chips
 
 # --- Import sources (git; phase 28, admin-managed since phase 35) ---