feat(editor): port geometry fix + type colours + endpoint editor + unsaved badge

Four operator-visible improvements in one cut.

Port geometry (the "connection dots don't line up with the
labels" bug):
 - Header now has a fixed two-line structure (title + 16-px
   subtitle slot) regardless of node kind, so the body's
   port-row Y-offsets are identical across step nodes and
   endpoint nodes.
 - NodeGeometry constants rewritten so the inline 8-px dot
   inside each port row and the 16-px canvas-side dot both
   compute to the same Y. Port rows now anchor where the
   eye expects them.

Port type colours:
 - Inputs endpoint labels carry `name: type` (e.g.
   `doc: bytes`), so the FlowNode body parses the type and
   tints the inline dot per type: text → primary,
   bytes/file → tertiary, json → secondary, number → amber,
   unknown → muted. Step input ports stay muted until a
   future commit can read module manifests for type info.

Endpoint editor:
 - Inputs and outputs nodes are now selectable. Selecting
   opens a dedicated editor in the properties panel:
   add / rename / retype / remove entries graphically
   instead of forcing the operator into the text tab.
   Inputs editor offers a Type dropdown
   (text / bytes / json / file / number);
   outputs editor exposes name + expression
   (e.g. `$step.field`).

Unsaved badge:
 - The toolbar's tiny 8-px dirty dot was easy to miss.
   Replace it with a coloured "unsaved" / "ungespeichert"
   chip + colour the file name itself in the primary accent
   when dirty. Operators see at a glance that a flow has
   unsaved changes, which matters because the Discard
   confirmation prompt won't fire if they don't realise
   they made changes.

Version 0.3.0 -> 0.4.0 — first new editor feature surface
since 0.3.

Signed-off-by: flemming-it <sf@flemming.it>

lib/src/flow_editor_page.dart

@@ -612,17 +612,44 @@ class _Toolbar extends StatelessWidget {
             style: theme.textTheme.titleSmall?.copyWith(
               fontFamily: 'monospace',
               fontWeight: FontWeight.w600,
+              // Dirty file name renders in the primary accent
+              // so the operator sees "this file has unsaved
+              // changes" at a glance even when their eye is
+              // elsewhere in the UI.
+              color: dirty ? theme.colorScheme.primary : null,
             ),
           ),
-          if (dirty)
-            Padding(
-              padding: const EdgeInsets.only(left: FaiSpace.xs),
-              child: Icon(
-                Icons.circle,
-                size: 8,
-                color: theme.colorScheme.primary,
+          if (dirty) ...[
+            const SizedBox(width: FaiSpace.xs),
+            Container(
+              padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 2),
+              decoration: BoxDecoration(
+                color: theme.colorScheme.primary.withValues(alpha: 0.14),
+                borderRadius: BorderRadius.circular(FaiRadius.sm),
+                border: Border.all(
+                  color: theme.colorScheme.primary.withValues(alpha: 0.4),
+                ),
+              ),
+              child: Row(
+                mainAxisSize: MainAxisSize.min,
+                children: [
+                  Icon(
+                    Icons.fiber_manual_record,
+                    size: 8,
+                    color: theme.colorScheme.primary,
+                  ),
+                  const SizedBox(width: 4),
+                  Text(
+                    strings.unsaved,
+                    style: theme.textTheme.labelSmall?.copyWith(
+                      color: theme.colorScheme.primary,
+                      fontWeight: FontWeight.w600,
+                    ),
+                  ),
+                ],
               ),
             ),
+          ],
           const Spacer(),
           FilledButton.tonalIcon(
             onPressed: onNew,