2g: advanced-mode highlight + engine.* wiring + matrix tests

Cross-cut verification matrix for ADR-0032 Phase 2 is now fully
populated with concrete test references — every row green. Filling
the matrix surfaced three real gaps that this commit closes.

1. Advanced-mode syntax highlighting (ADR-0030 §8 matrix row).
   The `ui.rs` Advanced branch routed through `plain_input_spans`,
   bypassing the highlight walker entirely. In production SQL
   keywords past the entry word rendered as plain identifiers.
   Fix: mode-aware variants of `highlight_runs`,
   `render_input_runs`, `lex_to_runs`, and `input_diagnostics`;
   the Advanced render path now uses the highlighted form with
   `Mode::Advanced`. `plain_input_spans` removed (unused).

2. Engine.* key wiring (ADR-0032 §11.4 / §13 matrix rows + handoff
   §3.3 follow-up). The four Phase-2 engine.* catalog entries
   were authored in 2d but never reached: `translate_generic`
   discarded the engine message and returned a vague catalog
   entry. Fix: pattern-match the engine message text for the four
   Phase-2 categories (aggregate misuse, group-by required,
   compound arity mismatch fallback, scalar-subquery cardinality)
   inside `translate_generic`, routing each to its engine-neutral
   catalog entry.

3. Matrix-coverage tests. Thirteen new tests covering the rows
   that had no explicit coverage:
   - 3 SQL keyword/operator/CASE highlight tests
   - 4 engine.* engine-message tests
   - 3 sql_expr column-completion tests (WHERE, HAVING)
   - 3 predicate-warning slot tests (CASE, ORDER BY, projection)
   - 1 all-10-playground-types recovery test (tests/sql_select.rs)

Plan document (docs/plans/20260520-adr-0032-phase-2.md) updated:
every (TBD) row in the cross-cut matrix replaced with a concrete
test file::function reference and a green status marker.

Test totals: 1428 → 1441 passing (+13 new). Clippy clean.

src/ui.rs

@@ -655,25 +655,25 @@ fn render_input_panel(app: &App, theme: &Theme, frame: &mut Frame<'_>, area: Rec
     // inverted so the cursor is visible without enabling a real
     // terminal cursor.
     //
-    // Simple-mode input gets per-token colouring (ADR-0022 §3)
-    // via input_render::render_input_runs. Advanced-mode input
-    // — DSL lexer doesn't speak SQL — renders plain (§12), with
-    // the same before/under/after cursor shape we always had.
+    // Per-token colouring (ADR-0022 §3 / ADR-0030 §8) in both
+    // modes — `render_input_runs_in_mode` runs the highlight
+    // walker with the active mode so SQL keywords / operators /
+    // CASE / function calls colour correctly in Advanced mode.
     let cursor = app.input_cursor.min(app.input.len());
-    let spans = match effective {
-        EffectiveMode::Simple => {
-            let runs = crate::input_render::render_input_runs(
-                &app.input,
-                cursor,
-                theme,
-                &app.schema_cache,
-            );
-            runs_to_spans(&app.input, &runs)
-        }
+    let mode_for_render = match effective {
+        EffectiveMode::Simple => crate::mode::Mode::Simple,
         EffectiveMode::AdvancedPersistent | EffectiveMode::AdvancedOneShot => {
-            plain_input_spans(&app.input, cursor, theme)
+            crate::mode::Mode::Advanced
         }
     };
+    let runs = crate::input_render::render_input_runs_in_mode(
+        &app.input,
+        cursor,
+        theme,
+        &app.schema_cache,
+        mode_for_render,
+    );
+    let spans = runs_to_spans(&app.input, &runs);
     // ADR-0027 §4: the rightmost six columns of the input row
     // (a five-column label plus a one-column gap) are reserved
     // unconditionally, so the text area is always
@@ -725,31 +725,6 @@ fn runs_to_spans<'a>(
         .collect()
 }
 
-/// Plain (no token highlighting) input rendering for advanced
-/// mode. Same before/under/after cursor shape as the
-/// pre-ADR-0022 input panel; here as a deliberate fallback.
-fn plain_input_spans<'a>(input: &'a str, cursor: usize, theme: &Theme) -> Vec<Span<'a>> {
-    let cursor = cursor.min(input.len());
-    let before = &input[..cursor];
-    let (under, after) = if cursor < input.len() {
-        let mut end = cursor + 1;
-        while end < input.len() && !input.is_char_boundary(end) {
-            end += 1;
-        }
-        (&input[cursor..end], &input[end..])
-    } else {
-        (" ", "")
-    };
-    vec![
-        Span::styled(before, Style::default().fg(theme.fg)),
-        Span::styled(
-            under,
-            Style::default().fg(theme.fg).add_modifier(Modifier::REVERSED),
-        ),
-        Span::styled(after, Style::default().fg(theme.fg)),
-    ]
-}
-
 fn render_hint_panel(app: &App, theme: &Theme, frame: &mut Frame<'_>, area: Rect) {
     let block = Block::default()
         .borders(Borders::ALL)