docs+code: rename tool labels everywhere

Sweep follow-up to 93e43fc. Display labels now consistent across docs,
landing pages, CLI output, code comments, docstrings, and test prose.
Five parallel surfaces touched:

- docs (EN + ES): README, USER-GUIDE, CLI-REFERENCE, and 11 internal
  design/planning docs
- landing pages: index + bookkeeper/revops/shopify-pet
- src: CLI module docstrings, _TOOL_DISPLAY dicts in cli_analyze.py
  and gui/components/_legacy.py, core module headers, every tool
  page's module docstring
- tests: class/method/module docstrings and section-header comments
- test-cases READMEs

Page slugs (1_Deduplicator etc.), tool_id strings (01_deduplicator
etc.), Python class names (TestDeduplicatorWorkflow, FeatureFlag.*),
URL paths, anchor IDs, CSS classes, and asset filenames were left
intact since they're code identifiers / structural references.

All 2033 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/DEVELOPER.md

@@ -33,7 +33,7 @@ CLI (src/cli*.py)         GUI (src/gui/app.py + pages/)
 | `core.errors` | `DataToolsError` hierarchy, `ensure_dataframe()`, `ensure_choice()`, `wrap_file_read/write()`, `format_for_user()` |
 | `core._constants` | `US_STATE_NAMES`, `US_STATE_CODES`, `USPS_EXPANSIONS`, `USPS_COMPRESSIONS` |
 
-## Data flow — Deduplicator
+## Data flow — Find Duplicates
 
 ```
 read_file()                       # auto-detect encoding, delimiter, header