fix(prompts): classify every sub-8B model (2b/4b/5b/6b) as SMALL

detect_model_size only matched 1b/3b/7b, so a genuinely small model such as
qwen*:4b fell through to LARGE and got the terse, less-guided prompt set it
can't follow — contributing to off-tone, rambling replies. Extend the small
patterns to cover all sub-8B sizes (1b-7b) across :/-/_ separators and sync the
spec table.

src/jarvis/reply/prompts/model_variants.py

@@ -22,11 +22,15 @@ class ModelSize(Enum):
     LARGE = "large"  # 8b+ - can infer tool usage from context
 
 
-# Model size patterns - models matching these are considered SMALL
+# Model size patterns - models matching these are considered SMALL.
+# Covers every sub-8B size (1b-7b): these models need the explicit, repeated
+# tool/greeting/instruction constraints and falter on the terse LARGE prompt.
+# Without 2b/4b/5b/6b here a genuinely small model (e.g. qwen*:4b) was
+# misclassified as LARGE and given the less-guided prompt set.
 _SMALL_MODEL_PATTERNS = (
-    ":1b", ":3b", ":7b",
-    "-1b", "-3b", "-7b",
-    "_1b", "_3b", "_7b",
+    ":1b", ":2b", ":3b", ":4b", ":5b", ":6b", ":7b",
+    "-1b", "-2b", "-3b", "-4b", "-5b", "-6b", "-7b",
+    "_1b", "_2b", "_3b", "_4b", "_5b", "_6b", "_7b",
     "gemma4",  # Gemma 4 - always small regardless of tag
 )