stack: Telemetrie-Default nach Installationsform, Byte-Deckel und Session-Retention (schliesst #55)

Files changed:
- .gitea/workflows/ci.yml
- .gitignore
- CHANGES.md
- EVALS.md
- INSTALL-MCP.md
- INSTALL.md
- VERSION
- instructions/setup-instance.md
- reports/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/doctor.py
- tools/chemenu/config.py
- tools/chemenu/mcp/server.py
- tools/chemenu/telemetry/policy.py
- tools/chemenu/telemetry/schema.py
- tools/chemenu/telemetry/writer.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_mcp_server.py
- tools/chemenu/tests/test_telemetry_emit.py
- tools/chemenu/tests/test_telemetry_policy.py
- tools/chemenu/version.py

.gitea/workflows/ci.yml

@@ -250,3 +250,11 @@ jobs:
           # A fresh instance owes no migration: dist export declares its content
           # version, so `status` must answer rather than ask for a baseline.
           tools/wikitool migrate status
+          # Telemetry defaults off for a distributed instance (the
+          # .wikitool-release.json this export carries), so nothing above
+          # should have created a trace tree at all - see EVALS.md § "Whether
+          # it runs at all".
+          if [ -e reports/telemetry ]; then
+            echo "reports/telemetry/ exists in a fresh distributed instance - telemetry should default off"
+            exit 1
+          fi