fix(config): deduplicate uniqueItems arrays before schema validation (#292)

* fix(config): deduplicate uniqueItems arrays before schema validation

When saving plugin config via the web UI, the form data is merged with
the existing stored config. If a user adds an item that already exists
(e.g. adding stock symbol "FNMA" when it's already in the list), the
merged array contains duplicates. Schemas with `uniqueItems: true`
then reject the config, making it impossible to save.

Add a recursive dedup pass that runs after normalization/filtering but
before validation. It walks the schema tree, finds arrays with the
uniqueItems constraint, and removes duplicates while preserving order.

Co-Authored-By: 5ymb01 <noreply@github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: recurse into array items and add tests for uniqueItems dedup

Address CodeRabbit review: _dedup_unique_arrays now also recurses into
array elements whose items schema is an object, so nested uniqueItems
constraints inside arrays-of-objects are enforced.

Add 11 unit tests covering:
- flat arrays with/without duplicates
- order preservation
- arrays without uniqueItems left untouched
- nested objects (feeds.stock_symbols pattern)
- arrays of objects with inner uniqueItems arrays
- edge cases (empty array, missing keys, integers)
- real-world stock-news plugin config shape

Co-Authored-By: 5ymb01 <noreply@github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: extract dedup_unique_arrays to shared validators module

Move _dedup_unique_arrays from an inline closure in save_plugin_config
to src/web_interface/validators.dedup_unique_arrays so tests import
and exercise the production code path instead of a duplicated copy.

Addresses CodeRabbit review: tests now validate the real function,
preventing regressions from diverging copies.

Co-Authored-By: 5ymb01 <noreply@github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: 5ymb01 <5ymb01@users.noreply.github.com>
Co-authored-by: 5ymb01 <noreply@github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web_interface/blueprints/api_v3.py

@@ -4612,6 +4612,13 @@ def save_plugin_config():
             seed_value = plugin_config['rotation_settings']['random_seed']
             logger.debug(f"After normalization, random_seed value: {repr(seed_value)}, type: {type(seed_value)}")
 
+        # Deduplicate arrays where schema specifies uniqueItems: true
+        # This prevents validation failures when form merging introduces duplicates
+        # (e.g., existing config has ['AAPL','FNMA'] and form adds 'FNMA' again)
+        if schema:
+            from src.web_interface.validators import dedup_unique_arrays
+            dedup_unique_arrays(plugin_config, schema)
+
         # Validate configuration against schema before saving
         if schema:
             # Log what we're validating for debugging