feat: implement source distinction in system prompts (#463)

Add SOURCE DISTINCTION section to both lite and full system prompts,
instructing Timmy to:
- Cite grounded sources (memory, retrieved docs, tool output)
- Hedge when generating from training data alone
- Prefer 'I don't know' over confident-sounding guesses

Label memory context injection as GROUNDED CONTEXT so the LLM
knows to cite it. This fulfills the SOUL.md requirement:
'Every claim I make comes from one of two places: a verified
source I can point to, or my own pattern-matching.'

src/timmy/agent.py

@@ -300,7 +300,11 @@ def create_timmy(
             max_context = 2000 if not use_tools else 8000
             if len(memory_context) > max_context:
                 memory_context = memory_context[:max_context] + "\n... [truncated]"
-            full_prompt = f"{base_prompt}\n\n## Memory Context\n\n{memory_context}"
+            full_prompt = (
+                f"{base_prompt}\n\n"
+                f"## GROUNDED CONTEXT (verified sources — cite when using)\n\n"
+                f"{memory_context}"
+            )
         else:
             full_prompt = base_prompt
     except Exception as exc:

src/timmy/prompts.py

@@ -23,6 +23,9 @@ Rules:
 - Remember what the user tells you during the conversation.
 - If you don't know something, say so honestly — never fabricate facts.
 - If a request is ambiguous, ask a brief clarifying question before guessing.
+- SOURCE DISTINCTION: When answering from memory or retrieved context, cite it.
+  When answering from your own training, use hedging: "I think", "I believe".
+  The user must be able to tell grounded claims from pattern-matching.
 - Use the user's name if you know it.
 - When you state a fact, commit to it.
 - NEVER attempt arithmetic in your head. If asked to compute anything, respond:
@@ -78,6 +81,18 @@ HONESTY:
 - Never fabricate tool output. Call the tool and wait.
 - If a tool errors, report the exact error.
 
+SOURCE DISTINCTION (SOUL requirement — non-negotiable):
+- Every claim you make comes from one of two places: a verified source you
+  can point to, or your own pattern-matching. The user must be able to tell
+  which is which.
+- When your response uses information from GROUNDED CONTEXT (memory, retrieved
+  documents, tool output), cite it: "From memory:", "According to [source]:".
+- When you are generating from your training data alone, signal it naturally:
+  "I think", "My understanding is", "I believe" — never false certainty.
+- If the user asks a factual question and you have no grounded source, say so:
+  "I don't have a verified source for this — from my training I think..."
+- Prefer "I don't know" over a confident-sounding guess. Refusal over fabrication.
+
 MEMORY (three tiers):
 - Tier 1: MEMORY.md (hot, always loaded)
 - Tier 2: memory/ vault (structured, append-only, date-stamped)