Read commands give wrong answers: impact misses attribute usage, describe fragment always fails, structure hides microflow counts, --json not pure

[ako]

Plan item 0.5 in PROPOSAL_mdl_beta_syntax_freeze.md §8.1. Found while orienting an agent on Evora Factory Management (1765 microflows).

1. describe fragment from page|snippet X widget Y always fails. The visitor sets ContainerType "PAGE"/"SNIPPET" (mdl/visitor/visitor_query.go:~994), but the executor switches on "page"/"snippet" (mdl/executor/cmd_fragments.go:84). The error message also omits the widget name.
2. structure -d 1 never shows microflow or nanoflow counts. It filters on MicroflowType = 'microflow' (mdl/executor/cmd_structure.go:69-70,192), but the catalog stores MICROFLOW/NANOFLOW.
3. search silently returns nothing when CATALOG.SOURCE is empty because no refresh catalog full source has run. It should say the source index is missing.
4. The refs graph has no attribute or enumeration-value targets. It also has no call workflow, widget→association or mapping→entity edges. As a result, impact Module.Entity.Attr reports "not referenced" for an attribute that is used. refs, impact and context repeat rows. The impact summary counts rows, not elements. context shows no related entities for an entity with 5 associations.
5. --json is not pure JSON. refs, callers and select print "Connected to…" and header lines on stdout. context ignores --json. search accepts both --format json and --json.
6. A stored expression's trailing newline is kept. describe then prints change $X (Status = …\n); with the ) on its own line.

Item 4 is the dangerous one. Split into PRs as needed, and follow /mxcli-dev:fix-issue for each.