refactor(gui): tool registry + components package for per-tool builds

Two low-risk seam moves to enable selling per-tool subsets without
breaking the existing all-in-one bundle. Behaviour identical; every
existing import still resolves; full pytest suite + every page returns
HTTP 200.

1. **Tool registry** (src/gui/tools_registry.py) — replaces the
   inline dict-of-dicts in app.py with a Tool dataclass and a TOOLS
   list. Adds a tier field ("core" today, "pro" / "enterprise" later)
   and tools_for_tier() / tool_by_id() / display_name() helpers. A
   per-tool build slices TOOLS at import time without code changes.

2. **components package** (src/gui/components/) — converts the former
   single components.py into a package with:
     _legacy.py        — original file, unchanged.
     __init__.py       — re-exports the legacy surface; existing
                         "from src.gui.components import …" calls
                         continue to work.
     shared.py         — hide_streamlit_chrome, pickup_or_upload
                         (every build needs these).
     gate.py           — require_normalization_gate (Pro / Suite SKUs).
     findings.py       — analyzer-finding widgets (drops out of a
                         standalone-Dedup build).
     dedup_review.py   — match-group cards + apply pipeline (drops out
                         of a non-dedup build).

   The seam modules are narrow re-exports today. As code migrates out
   of _legacy.py into the focused modules, the public import path
   stays stable via the shim.

E2E: 765 passed, 17 xfailed (unchanged); home page + all 9 tool pages
+ Review page render HTTP 200; full pipeline (analyze → auto_fix →
apply_decisions → output bytes) round-trips on the kitchen-sink
fixture with zero high-confidence findings remaining post-fix.

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

src/gui/components/__init__.py

@@ -0,0 +1,57 @@
+"""Reusable Streamlit widgets for the DataTools GUI.
+
+This package replaces the former single ``components.py`` module. Public
+behaviour is identical — every name that used to be importable from
+``src.gui.components`` is still importable from the same path because
+this ``__init__`` re-exports the legacy surface in full.
+
+The package layout exists so per-tool builds can ship only the seams
+they need without dragging the entire kitchen-sink module:
+
+    components/
+        __init__.py        ← compatibility shim (this file)
+        _legacy.py         ← original components.py, unchanged
+        gate.py            ← gate-only seam (require_normalization_gate)
+        findings.py        ← analyzer-finding rendering seam
+        dedup_review.py    ← dedup match-group cards + review pipeline
+        shared.py          ← chrome / file-pickup helpers used by every tool
+
+A standalone Deduplicator build, for example, can ship without
+``findings.py`` and ``gate.py`` — those modules import the analyzer /
+gate code that the Lite SKU does not include.
+
+Adding new tooling: drop new helpers into the appropriate seam module.
+Add their names to its ``__all__`` and to this file's ``__all__`` if
+they should remain importable from ``src.gui.components`` directly.
+"""
+
+from __future__ import annotations
+
+# Re-export the full legacy surface so existing pages continue to
+# import unchanged. Once individual tool packages start consuming
+# the focused seam modules directly, names can migrate out of
+# _legacy.py without breaking those imports — this shim is what
+# absorbs the move.
+from ._legacy import *  # noqa: F401,F403
+from . import _legacy as _legacy  # noqa: F401  (keep for direct access)
+
+# Names exported from _legacy.py that pages currently use. Kept here as
+# the canonical public list so a removal from _legacy is a visible
+# breaking change instead of a silent drop.
+__all__ = [
+    # Shared chrome / pickup / gate
+    "hide_streamlit_chrome",
+    "pickup_or_upload",
+    "require_normalization_gate",
+    # Dedup widgets
+    "config_panel",
+    "match_group_card",
+    "results_summary",
+    "apply_review_decisions",
+    # Analyzer widgets
+    "tool_display_name",
+    "render_findings_panel",
+    "render_hidden_aware_preview",
+    "upload_and_analyze_section",
+    "findings_count_for_tool",
+]