ADR-0017 implementation: per-cell type-change with override flags

Replaces the placeholder "trust STRICT" body of do_change_column_type
with the per-cell transformer matrix from ADR-0017. Adds:

- src/type_change.rs: CellOutcome { Clean / Lossy / Incompatible }
  + transform_cell + static_refusal covering every matrix pair
  from §3 (54 unit tests).
- --force-conversion and --dont-convert flags on `change column`
  (mutually exclusive at parse time per §5).
- Refined PK rule (§4.1): refused only when the column has an
  inbound FK and fk_target_type would change. Outbound-FK columns
  still refused outright (§4.2). PK / shortid uniqueness checked
  post-transformation (§4.3).
- Bordered diagnostic tables (lossy / incompatible / collision)
  via the pretty-table renderer (§7) — uses ADR-0016's primitives.
- [client-side] success note (§6) when any cell was rewritten.
- Friendly wrapper for engine-level errors under --dont-convert
  so no engine vocabulary leaks (ADR-0002 user-facing posture).

ADR-0017 §3 + §7 amended in place (with user sign-off): serial->int
added explicitly to the always-clean matrix, and diagnostic rows
identify themselves by PK value(s) rather than positional indices
(SQLite returns rows unordered without ORDER BY, so positional
"row 5" is unaddressable).

Tests: 449 -> 517 (+68). Clippy clean with nursery lints.

src/app.rs

@@ -13,7 +13,8 @@ use tracing::{trace, warn};
 
 use crate::action::Action;
 use crate::db::{
-    CascadeEffect, DataResult, DeleteResult, InsertResult, TableDescription, UpdateResult,
+    CascadeEffect, ChangeColumnTypeResult, DataResult, DeleteResult, InsertResult,
+    TableDescription, UpdateResult,
 };
 use crate::dsl::{Command, ParseError, parse_command};
 use crate::event::AppEvent;
@@ -312,6 +313,10 @@ impl App {
                 self.handle_dsl_delete_success(&command, &result);
                 Vec::new()
             }
+            AppEvent::DslChangeColumnSucceeded { command, result } => {
+                self.handle_dsl_change_column_success(&command, result);
+                Vec::new()
+            }
             AppEvent::DslFailed { command, error } => {
                 self.handle_dsl_failure(&command, &error);
                 Vec::new()
@@ -761,6 +766,43 @@ impl App {
         }
     }
 
+    fn handle_dsl_change_column_success(
+        &mut self,
+        command: &Command,
+        result: ChangeColumnTypeResult,
+    ) {
+        let summary = format!("[ok] {} {}", command.verb(), command.display_subject());
+        self.note_system(summary);
+        if let Some(note) = result.client_side {
+            // ADR-0017 §6: pedagogical hook telling the learner
+            // "the tool did this for you; raw SQL would need a
+            // CAST or application-level code." Lossy variant
+            // adds the lossy count when --force-conversion was
+            // used.
+            let line = if note.lossy > 0 {
+                format!(
+                    "[client-side] {n} row(s) transformed; {l} of those discarded \
+                     information (lossy). In raw SQL this would need an explicit \
+                     `CAST` or application-level code.",
+                    n = note.transformed,
+                    l = note.lossy
+                )
+            } else {
+                format!(
+                    "[client-side] {n} row(s) were transformed before being stored. \
+                     In raw SQL this would need an explicit `CAST` or \
+                     application-level code.",
+                    n = note.transformed
+                )
+            };
+            self.note_system(line);
+        }
+        for line in crate::output_render::render_structure(&result.description) {
+            self.note_system(line);
+        }
+        self.current_table = Some(result.description);
+    }
+
     fn handle_dsl_delete_success(&mut self, command: &Command, result: &DeleteResult) {
         self.note_system(format!(
             "[ok] {} {}",