Replaces the placeholder pipe-and-dash output with Unicode
box-drawing tables for both data results and table-structure
listings, per ADR-0016.
* New `src/output_render.rs` module with `render_data_table`
and `render_structure`. Hand-rolled to match the project's
existing CSV/YAML pattern; ~300 lines.
* Header-only outer-frame border style: outer ┌─┐│└─┘ box +
├─┤ header underline, no per-row separators. NULL renders
as `(null)`; cell newlines/tabs/control chars become
`↵`/`→`/`·` as display-only substitutions.
* Type-aware column alignment: numeric types right-aligned,
everything else left. `DataResult` gains a `column_types:
Vec<Option<Type>>` field, populated from the existing
metadata lookup at the two query sites in db.rs (no new
query paths).
* Structure view shows Name | Type | Constraints columns;
References / Referenced-by sections retain plain-text
format, leaving room for the future relationship-rendering
ADR.
* 18 new unit tests in output_render.rs (plus 4 insta
snapshots for the canonical layouts). Existing assertions
in app.rs and walking_skeleton.rs updated to match the new
format.
Total: 426 passing, 0 failing, 0 skipped (up from 408).
Clippy clean.
claude@clouddev1