docs: enrich docs/specs and remove placeholders

**Motivations:**
- Make docs/specs implementation-ready without empty sections or placeholders.

**Root causes:**
- Multiple specs still contained non-actionable placeholders (N/A, “see above”, "..."), and inconsistent “no cache” wording.

**Correctifs:**
- Replace placeholders with explicit tables, structures, and typed examples.
- Align “no cache / no memorization” statements where relevant.

**Evolutions:**
- Add a features doc entry to track the documentation enrichment effort.

**Pages affectées:**
- docs/specs/*
- docs/features/docs-specs-enrichment.md
- docs/leo.md
- docs/plan-enrich-docs-specs.md

docs/specs/achat_upgrade_case_zoo.md

@@ -16,7 +16,7 @@ Action sur l'objet `Zoo` (dimensions).
   "zoo_id": "uuid",
   "dimensions": { "width": 5, "height": 6 },
   "expansion_history": [
-    { "direction": "EAST", "cost": 1000, "timestamp": "..." }
+    { "direction": "EAST", "cost": 1000, "timestamp": "timestamp" }
   ],
   "max_dimensions": { "width": 20, "height": 20 }
 }