feat: project chip + file-wins guard (multi-project stage 2)

When the open flow declares its own top-level project:, show it as a
chip in the tab action strip. On mismatch with the host's active
workspace, an amber file-wins pill offers a one-click Switch to
<project> — the file always wins for the run; switching only aligns
the workspace view.

New optional FlowEditorPage.activeProject + onSwitchToFileProject.
Parse + normalize (mirrors the hub's normalize_project_slug) lives in
flow_project.dart, unit-tested. flutter analyze clean, 57 tests green.

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

lib/src/flow_project.dart

@@ -0,0 +1,50 @@
+/// Parsing + normalization for a flow file's own top-level
+/// `project:` key. Kept separate from the page so the "file wins"
+/// semantics are unit-testable without pumping the whole editor.
+///
+/// Mirrors the hub's `resolve_project` (file's `project:` is the
+/// run's project unless the caller overrides it) and
+/// `normalize_project_slug`, so the chip the editor shows compares
+/// equal to what the hub actually stamps.
+library;
+
+/// The flow's own top-level `project:` slug (normalized), or empty
+/// when the YAML declares none. Only a *non-indented* `project:`
+/// line counts — a nested `project:` inside a step's `with:` block
+/// is ignored.
+String parseFlowProject(String yaml) {
+  for (final raw in yaml.split('\n')) {
+    if (raw.startsWith(' ') || raw.startsWith('\t')) continue;
+    final m = RegExp(r'^project:\s*(.+?)\s*$').firstMatch(raw);
+    if (m != null) {
+      final value = m.group(1)!.replaceAll(RegExp('''^["']|["']\$'''), '');
+      return normalizeProjectSlug(value);
+    }
+  }
+  return '';
+}
+
+/// Mirror of the hub's `normalize_project_slug`: lowercase,
+/// collapse spaces/underscores/dashes to a single `-`, drop
+/// everything else, trim trailing dashes. Empty in → empty out
+/// (the editor treats "no project" and "blank project" alike).
+String normalizeProjectSlug(String raw) {
+  final buf = StringBuffer();
+  var prevDash = false;
+  for (final ch in raw.trim().toLowerCase().split('')) {
+    if (RegExp(r'[a-z0-9]').hasMatch(ch)) {
+      buf.write(ch);
+      prevDash = false;
+    } else if ((ch == ' ' || ch == '_' || ch == '-') &&
+        !prevDash &&
+        buf.isNotEmpty) {
+      buf.write('-');
+      prevDash = true;
+    }
+  }
+  var out = buf.toString();
+  while (out.endsWith('-')) {
+    out = out.substring(0, out.length - 1);
+  }
+  return out;
+}