fix(deriver): stop extraction examples teaching fabricated inferences

The EXAMPLES block in the minimal deriver prompt demonstrated two
inferences that its own output schema forbids:

- "I just had my 25th birthday last Saturday" -> "alice's birthday is
  June 21st". A vague relative reference cannot yield a specific date;
  this demonstrates inventing one.
- "I took my dog for a walk in NYC" -> "alice lives in NYC". Visiting a
  place is not living there.

A third example invited "+ general knowledge" inference to produce a
deductive conclusion. The deriver has no channel for that output --
PromptRepresentation carries only `explicit`, described as "direct
quotes or clear paraphrases only, no interpretation or inference", and
deductive conclusions are produced by the Dreamer's DeductionSpecialist.

Replace all three with examples that stay inside the schema's contract.
The dog/NYC message is kept and shown extracting correctly, and a third
example shows that "lives in NYC" is valid when actually stated, so the
examples teach the boundary rather than just avoiding it.

Closes #626

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/deriver/prompts.py

@@ -72,9 +72,9 @@ RULES:
 - Contextualize each observation sufficiently (e.g. "Ann is nervous about the job interview at the pharmacy" not just "Ann is nervous")
 
 EXAMPLES (using `alice` as the target peer id):
-- EXPLICIT: "I just had my 25th birthday last Saturday" → "alice is 25 years old", "alice's birthday is June 21st"
-- EXPLICIT: "I took my dog for a walk in NYC" → "alice has a dog", "alice lives in NYC"
-- EXPLICIT: "alice attended college" + general knowledge → "alice completed high school or equivalent"
+- EXPLICIT: "I just turned 25" → "alice is 25 years old"
+- EXPLICIT: "I took my dog for a walk in NYC" → "alice has a dog", "alice walked her dog in NYC"
+- EXPLICIT: "I've lived in NYC for six years" → "alice lives in NYC"
 
 {custom_instructions_section}