feat(seed): --seed flag, ambient wiring, and /runda hardening (ADR-0048 P1.4 + DA)

P1.4 — user-visible surface:
- Grammar: `seed <table> [count] [--seed <n>]` (the first DSL flag with a
  value); build_seed disambiguates the seed value from the positional count.
- Verified the auto-wired surface: table-name completion, --seed offered as
  a candidate, validity consistent with `show data`, an ADR-0042 near-miss
  row for bare `seed`, and render tests for the seed outcome.

/runda hardening — eight DA findings, all resolved:
- FK sampling now uses ORDER BY so --seed reproducibility no longer relies
  on SQLite's unspecified DISTINCT order (D4).
- shortid columns now generate from seed's seeded RNG (new
  shortid::generate_with_rng) — D4 now holds with no exceptions.
- Added the missing coverage the DA flagged: undo-one-step (D15), replay
  re-runs a seed line (D16), advanced-mode (D5), atomic rollback on a
  constraint failure, seed 0 no-op, complex-CHECK advisory (D17), and
  FK + shortid reproducibility.

2358 pass / 0 fail / 0 skip, clippy all-targets clean.

src/app.rs

@@ -6258,6 +6258,76 @@ mod tests {
         );
     }
 
+    #[test]
+    fn seed_success_renders_count_preview_and_advisory() {
+        // ADR-0048: handle_dsl_seed_success renders the seeded-row count,
+        // the preview table, and the enum/CHECK advisory.
+        let mut app = App::new();
+        app.output
+            .push_back(OutputLine::echo("seed users 20", crate::mode::Mode::Simple));
+        app.update(AppEvent::DslSeedSucceeded {
+            command: Command::Seed {
+                table: "users".to_string(),
+                count: Some(20),
+                rng_seed: None,
+            },
+            result: crate::db::SeedResult {
+                table: "users".to_string(),
+                requested: 20,
+                produced: 20,
+                data: crate::db::DataResult {
+                    table_name: "users".to_string(),
+                    columns: vec!["name".to_string()],
+                    column_types: vec![None],
+                    rows: vec![vec![Some("Alice".to_string())]],
+                },
+                advisory_columns: vec!["status".to_string()],
+            },
+        });
+        let texts: Vec<String> = app.output.iter().map(|l| l.text.clone()).collect();
+        assert!(
+            texts.iter().any(|t| t.contains("20 row(s) seeded into users")),
+            "seeded-row count surfaced: {texts:?}",
+        );
+        assert!(
+            texts.iter().any(|t| t.contains("status") && t.contains("generic text")),
+            "the advisory names the enum-ish column: {texts:?}",
+        );
+    }
+
+    #[test]
+    fn seed_success_reports_a_cap() {
+        // produced < requested → the cap note appears next to the count.
+        let mut app = App::new();
+        app.output
+            .push_back(OutputLine::echo("seed J 10", crate::mode::Mode::Simple));
+        app.update(AppEvent::DslSeedSucceeded {
+            command: Command::Seed {
+                table: "J".to_string(),
+                count: Some(10),
+                rng_seed: None,
+            },
+            result: crate::db::SeedResult {
+                table: "J".to_string(),
+                requested: 10,
+                produced: 4,
+                data: crate::db::DataResult {
+                    table_name: "J".to_string(),
+                    columns: Vec::new(),
+                    column_types: Vec::new(),
+                    rows: Vec::new(),
+                },
+                advisory_columns: Vec::new(),
+            },
+        });
+        let texts: Vec<String> = app.output.iter().map(|l| l.text.clone()).collect();
+        assert!(
+            texts.iter().any(|t| t.contains("4 row(s) seeded into J")
+                && t.contains("of 10 requested")),
+            "the cap note surfaces requested vs produced: {texts:?}",
+        );
+    }
+
     #[test]
     fn sql_delete_returning_renders_cascade_and_result_table() {
         // ADR-0033 3g: a DELETE … RETURNING surfaces BOTH the cascade