docs: update all documentation to reflect v3.0 functionality

Update README, CLI reference, and developer guide to cover delimiter
selector, inline checkboxes/dropdowns, live surviving rows preview,
multi-row survivors, and apply_review_decisions(). Remove dead link.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/DEVELOPER.md

@@ -90,17 +90,20 @@ Typer-based CLI with 17 options. Key responsibilities:
 ### src/gui/app.py — Streamlit GUI
 
 Single-page layout:
-- File upload with instant preview
+- File upload with instant preview and configurable delimiter (comma, tab, semicolon, pipe, or custom)
 - Advanced options expander (column selection, fuzzy, normalizers, survivor rule, merge, config profiles)
 - Find Duplicates button → runs `deduplicate()` with `progress_callback`
-- Interactive review: expandable match group cards with merge/keep/skip buttons
+- Interactive review via `st.data_editor` with inline checkboxes and column dropdowns
+- Batch actions: Accept All, Reject All, Clear Decisions
+- Apply review decisions and download cleaned results
 - Download buttons for deduplicated CSV, removed rows, and match groups report
 
 ### src/gui/components.py — Reusable GUI Widgets
 
-- **`match_group_card()`** — expandable card showing side-by-side row comparison with diff highlighting
-- **`config_panel()`** — the advanced options expander, returns a `DeduplicationConfig`
-- **`results_summary()`** — summary stats and download buttons
+- **`match_group_card()`** — expandable card with `st.data_editor`: inline Keep checkboxes per row, `SelectboxColumn` dropdowns for differing columns, and a live surviving rows preview
+- **`config_panel()`** — the advanced options expander, returns settings dict with strategies, survivor rule, merge flag
+- **`results_summary()`** — summary metrics and download buttons
+- **`apply_review_decisions()`** — builds final DataFrames from user review decisions (merge, split, or keep-all per group) with column override support
 
 ## Data Flow