rename: TopologyGraph -> BRepGraph, bump OCCTSwift floor to 1.15.0

[gsdali]

Summary

OCCTSwift renamed its Swift wrapper class TopologyGraph -> BRepGraph to
match the C++ package it wraps (SecondMouseAU/OCCTSwift#335, shipped in
v1.15.0),
leaving a deprecated typealias so downstream consumers keep compiling with
a warning. Tracked here as #78.

This PR does the mechanical migration:

• OCCTSwift floor bumped 1.12.9 -> 1.15.0 (Package.swift). The bare
  BRepGraph symbol doesn't exist before 1.15.0 (only the deprecated
  TopologyGraph typealias does, and only from that release forward), so
  once our own code stops using the deprecated name the floor has to
  guarantee the new symbol is actually present — the previous open
  from: "1.12.9" range technically permitted 1.15.0 but didn't require it.
  Package.resolved refreshed accordingly (occtswift 1.8.0 -> 1.15.0; the
  rest of the cohort floats up within their existing open floors: AIS 1.0.5,
  IO 1.0.2, Mesh 1.1.6, Tools 1.3.1, Viewport 1.1.24 — no manifest changes
  needed for those, already-open ranges).

• TopologyGraph -> BRepGraph across every real reference (re-grepped
  the whole tree rather than trusting the tracking issue's file list
  verbatim, which turned up a few more spots than originally filed):

  • Sources/ScriptHarness/BREPGraphJSONExporter.swift
  • Sources/ScriptHarness/BREPGraphSQLiteExporter.swift
  • Sources/ScriptHarness/GraphIO.swift
  • Sources/ScriptHarness/ScriptContext.swift
  • Sources/occtkit/Commands/GraphSelect.swift
  • Sources/occtkit/Commands/GraphML.swift
  • Sources/GraphML/main.swift
  • Package.swift (comment)
  • CLAUDE.md (dependency-floor writeup + a Key Conventions bullet)
  • README.md (Requirements table floor bump)
  • docs/guides/architecture.md
  • docs/reference/topology-graph.md, docs/reference/script-harness.md,
    docs/reference/ScriptHarness.md, docs/reference/occtkit-verbs.md
  • docs/guides/cookbook/topology-graph.md

  Left the "Topology graph" CLI-verb-family name untouched (page titles,
  topology-graph.md filenames, the graph-validate/compact/dedup/
  query/ml/select verb-group prose) — that's this repo's own product
  terminology for a command family, distinct from the OCCTSwift class name.
  docs/reference/introspection.md already shows the two coexisting
  ("Topology graph family" alongside "BRepGraph output") from before this
  PR, which is the pattern followed here. Pure identifier rename otherwise —
  no behavior change.

Pairs with OCCTSwift#335 / v1.15.0.

Test plan

• swift package resolve (after deleting Package.resolved) — resolves
  OCCTSwift at 1.15.0
• swift build — clean, 0 errors, 0 warnings
• swift build --build-tests — clean, 0 errors, 0 warnings
• swift test — 3/3 tests pass (DrawingComposerTests; this repo has no
  dedicated test target over ScriptHarness/graph exporters, per
  CLAUDE.md's "No tests exist" note for that area)
• Manual smoke test against recipes/01-mounting-bracket/output.brep:
  occtkit graph-validate, occtkit graph-select --query face-adjacency,
  occtkit graph-ml, and the standalone GraphML target all run and
  produce correct output against the rebuilt BRepGraph path

Version

Latest tag is v1.4.6. This repo's own convention (per its release history)
treats floor bumps that are required by an actual API/behavior change as
minor bumps (e.g. v1.1.0 for the OCCTSwift 1.7.1 floor), reserving patch
bumps for same-API crash-fix repins (v1.4.3-v1.4.6). Since this floor bump is
required by the renamed symbol rather than being a drop-in crash fix, I'd
suggest v1.5.0 as the next tag — but leaving the tag/release itself to
the maintainer, per usual.

Closes #78

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