* Add cost basis tracking and management to holdings
- Added migration to introduce `cost_basis_source` and `cost_basis_locked` fields to `holdings`.
- Implemented backfill for existing holdings to set `cost_basis_source` based on heuristics.
- Introduced `Holding::CostBasisReconciler` to manage cost basis resolution logic.
- Added user interface components for editing and locking cost basis in holdings.
- Updated `materializer` to integrate reconciliation logic and respect locked holdings.
- Extended tests for cost basis-related workflows to ensure accuracy and reliability.
* Fix cost basis calculation in holdings controller
- Ensure `cost_basis` is converted to decimal for accurate arithmetic.
- Fix conditional check to properly validate positive `cost_basis`.
* Improve cost basis validation and error handling in holdings controller
- Allow zero as a valid cost basis for gifted/inherited shares.
- Add error handling with user feedback for invalid cost basis values.
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Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>
