feat(nodes): per-node Save to library switch (#90)

Every PromptManager node (Classic, Text, Focused, Split, Pair) gets an
optional save_to_library BOOLEAN, default on and declared last. Off, the
node still returns its normal outputs but PromptManager ignores the run:

- the node saves, counts, tracks and records nothing;
- the queue hook reads the switch from the queued graph (literal, or a
  linked PrimitiveBoolean), so a cached node is not counted either; a
  switch wired from an unreadable node is left to the node itself;
- an opted-out node is no run prompt, so no tracker entry, run key,
  embedded-metadata match or history attribution links its images, and
  a run with any opted-out positive node links none of its files;
- the scan reports such files as not_saved (never stored or queued for
  Needs review), and a file whose only opted-out node is its negative is
  stored positive-only, without the pair;
- execution history records no prompt text for an opted-out role.

PromptSearchList only reads the library and gets no switch.

The switch takes the widget index older workflows used for the editor's
own DOM slot (''), so a configure step turns any non-boolean value on:
workflows saved before the switch load with it on and no earlier widget
value moves. The Focused, Split and Pair editors draw it as a "Save to
library" checkbox in their toolbar; Classic and Text show the native
toggle.

utils/execution_context_graph.py

@@ -3,8 +3,13 @@
 import re
 from dataclasses import dataclass
 from .execution_contexts import PromptSnapshot, TextEvidence, text_size
+from .prompt_graph import save_setting
 from .prompt_pair_resolver import _DEFAULT_ADAPTERS
 
+# A role whose PromptManager source has save_to_library off, or wired from a
+# node the graph cannot read: no text is recorded for it (#90)
+NOT_SAVED = "not_saved"
+
 
 @dataclass(frozen=True)
 class SourceRef:
@@ -332,6 +337,11 @@ class _Projector:
             self.transformed = False
             # Only the capture-source-to-consumer path determines transforms.
             sources = self.discover_sources(value, "conditioning")
+            if any(
+                save_setting(self.graph, source.node_id) is not True
+                for source in sources
+            ):
+                return GraphRole((), None, NOT_SAVED)
             snapshot, _ = self.text(value, "conditioning")
             return GraphRole(
                 sources, snapshot, "source-transformed" if self.transformed else ""