Phase 8b-Lite: pipe-operator chaining for named parameters

Adds `operator|` in `namespace CGAL` so package-local named parameters
can be combined left-to-right without modifying CGAL upstream:

    auto p = CGAL::parameters::gradient_tolerance(1e-12)
           | CGAL::parameters::max_iterations(500)
           | CGAL::parameters::output_uv_map(uv);
    CGAL::discrete_conformal_map_euclidean(mesh, p);

Why not the canonical `.a().b().c()` syntax
───────────────────────────────────────────
CGAL's standard chaining mechanism requires registering each named
parameter as a member function on `Named_function_parameters` via the
`CGAL_add_named_parameter` macro in
`CGAL/STL_Extension/internal/parameters_interface.h` — a vendored
upstream file that conformallab++ deliberately treats as read-only.

Adding member-function chainers for our package-local tags would
require either forking CGAL or modifying the vendored copy.  Neither
is acceptable for a library that wants to remain portable across
future CGAL releases.

The pipe-operator achieves the same compositional semantics via a
free function in `namespace CGAL` (so ADL finds it for
`Named_function_parameters` operands).  Implementation: rebuild the
right-hand-side `Named_function_parameters` with the left-hand-side
as its `Base`, producing an indistinguishable chain that every entry
function accepts unchanged.

Implementation: `code/include/CGAL/Conformal_map/internal/parameters.h`
lines 158-187.  The operator is constrained to right-hand-sides with
`No_property` base (i.e. fresh single-parameter packs from the helper
functions), so it never collides with any future CGAL operator on the
same type.

Tests (2 new, total Phase-8b-Lite suite 15 → 17)
────────────────────────────────────────────────
* CGALPhase8bLite.NamedParamPipe_MultipleParamsTakeEffect
    Chain three parameters; verify all three take effect (tight
    tolerance respected + UV pmap populated + iteration cap honoured).
* CGALPhase8bLite.NamedParamPipe_TwoParams
    Chain two parameters; verify max_iterations(0) blocks the loop
    even when combined with another param.

Full CGAL suite: 234/234 PASSED, 0 SKIPPED (was 232).
Total: 257/257 PASSED, 0 SKIPPED (was 255).
scripts/check-test-counts.sh: OK.

Documentation updates
─────────────────────
* doc/tutorials/add-output-uv-map.md §3.4: "Current limitation: no
  chaining" → "Chaining: use the pipe operator `|`".  Explains why
  CGAL's `.member()` syntax isn't available and shows the `|`
  workaround with a working code example.
* doc/architecture/locked-vs-flexible.md §8: chaining now flagged as
  shipped via pipe; recommended posture says `.member()` chaining
  only if a user pushes for the CGAL-canonical syntax.
* doc/roadmap/porting-status.md §5: API limitations table updated.
* doc/api/tests.md: CGALPhase8bLite row 15 → 17, total 232 → 234.

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

code/tests/cgal/test_cgal_phase8b_lite.cpp

@@ -322,3 +322,51 @@ TEST(CGALPhase8bLite, OutputUvMap_NormaliseLayout_TakesEffect)
         EXPECT_TRUE(std::isfinite(uv_norm[v].x()));
     }
 }
+
+// ════════════════════════════════════════════════════════════════════════════
+// 7.  Named-parameter chaining via pipe-operator
+//
+// CGAL's `.a().b().c()` chaining requires modifying CGAL upstream, which
+// we don't do.  conformallab++ provides a `|` operator that achieves the
+// same effect by left-to-right composition.  These tests verify that the
+// chain is read back correctly by the entry functions.
+// ════════════════════════════════════════════════════════════════════════════
+
+TEST(CGALPhase8bLite, NamedParamPipe_MultipleParamsTakeEffect)
+{
+    using K = CGAL::Simple_cartesian<double>;
+    auto mesh = make_quad_strip();
+
+    auto uv = mesh.add_property_map<Vertex_index, K::Point_2>(
+        "v:pipe_uv", K::Point_2(0, 0)).first;
+
+    // Chain three parameters using `|`.
+    auto params = CGAL::parameters::gradient_tolerance(1e-12)
+                | CGAL::parameters::max_iterations(500)
+                | CGAL::parameters::output_uv_map(uv);
+
+    auto res = CGAL::discrete_conformal_map_euclidean(mesh, params);
+
+    EXPECT_TRUE(res.converged);
+    EXPECT_LT(res.gradient_norm, 1e-10);   // tight tolerance applied
+    EXPECT_LE(res.iterations, 500);
+    // UV pmap was populated.
+    bool any_nonzero = false;
+    for (auto v : mesh.vertices()) {
+        if (std::abs(uv[v].x()) + std::abs(uv[v].y()) > 1e-10) {
+            any_nonzero = true;
+            break;
+        }
+    }
+    EXPECT_TRUE(any_nonzero);
+}
+
+TEST(CGALPhase8bLite, NamedParamPipe_TwoParams)
+{
+    // Pipe two parameters and verify both take effect.
+    auto mesh = make_triangle();
+    auto params = CGAL::parameters::max_iterations(0)
+                | CGAL::parameters::gradient_tolerance(1e-6);
+    auto res = CGAL::discrete_conformal_map_euclidean(mesh, params);
+    EXPECT_EQ(res.iterations, 0);   // max_iterations(0) blocks the loop
+}