fix: dirty detection — compare fullText, snapshot after load

Stefan reported false-positive "Discard unsaved changes?"
dialogs when clicking around in the file list. Cause: the
naive `_code.text == _loadedText` check fired stale even
right after _code.text = text, because CodeController
silently rewrites the visible text during the assignment
(trailing-newline normalisation, fold marker insertion on
some YAML constructs, …) so _code.text deviated from the
just-stored _loadedText immediately.

Fix:
  * Drop `_loadedText` field, replace with `_baseline`.
  * Set `_code.text = ...` first (outside setState), then
    capture `_baseline = _code.fullText` inside setState.
    fullText is the canonical post-processed value, not the
    visible-after-folding text — comparing fullText against
    fullText eliminates the spurious diff.
  * _dirty getter now compares `_code.fullText != _baseline`.

Applied to all four load / save / new-flow sites.

Bump version 0.1.0 → 0.1.1. Studio's pubspec already pins
`ref: main` so the next `flutter pub get` picks the fix up.

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

pubspec.yaml

@@ -1,6 +1,6 @@
 name: fai_studio_flow_editor
 description: Swappable inline YAML editor for F∆I Studio flows.
-version: 0.1.0
+version: 0.1.1
 publish_to: 'none'
 repository: https://git.flemming.ai/fai/studio-flow-editor