feat(server): settings pack — 22 environment tools behind TOOL_PACKS, lean grows to 55, three groups, golden set +10

Task 24 (merge sanity) on main after the five track E groups merged.

- TOOL_PACK_NAMES = ("core", "pid", "settings"); PACK_TOOL_NAMES["settings"]
  is exactly the 22 SECTION 20 tools. Styles and page setup stay in core.
- LEAN_TOOL_NAMES += page_setup_apply, batch_plot (53 -> 55).
- _GROUP_TAG_PRIORITY / _GROUP_TAG_LABELS: "style" moved up next to "pid",
  "pagesetup" -> page_setup and "environment" -> environment added; the 28
  SECTION 19/20 decorators gain their section tag, so _tool_groups() reports
  styles 10 / page_setup 6 / environment 22 (23 groups, 204 tools) and
  pack == group == section for the settings pack.
- SECTION headers, backends/base.py composition, contracts/__init__.py
  exports and the layer_states feature entry were already correct after the
  merge (read and confirmed, nothing edited).
- Pack text: config.py, .env.example, README config row; README <sub> line
  204 tools in 23 groups; release snapshot 3259 collected tests (measured).
- docs/tool-inventory.json regenerated; registry snapshot re-derived.
- tests: test_tool_packs.py replaced (11 tests), test_capability_contract.py
  +3 (composition, the agreed capability flags, layer_states honesty),
  golden set +10 tuning cases (81 = 66 tuning + 15 holdout); all ten route
  in the top 3 without alias edits.

Deviation from the plan text: TRACK_E_KEYS carries five keys, not six. The
plan's "mleaderstyle" (ezdxf True / com False) contradicts spec §8.1, which
retracted that key because the ActiveX route exists (§4.2); measured on the
tree: capability_keys() == {boundary_trace, chspace, interactive_prompt,
live_application, preferences, revcloud, wipeout}, and
ComBackend.mleaderstyle_create is a native implementation
(backends/com_backend.py:6752, is_capability_default -> False). The test now
also asserts the key is absent.

No new ActiveX call was written in this task, so no live probe was needed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

.env.example

@@ -55,7 +55,7 @@ DANGEROUS_COMMANDS_ENABLED=false
 # still boots, falling back to full with a warning.
 TOOL_PROFILE=full
 
-# Tool packs: all (default) | comma list of core,pid — advertise only the
+# Tool packs: all (default) | comma list of core,pid,settings — advertise only the
 # vertical packs this client uses. core is always on.
 TOOL_PACKS=all