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>

doc/tutorials/add-output-uv-map.md

@@ -157,28 +157,38 @@ canonical post-processing pass:
 
 Default: `false`. Has no effect unless `output_uv_map` is also passed.
 
-### Current limitation: no chaining
+### Chaining: use the pipe operator `|`
 
-The CGAL machinery supports chaining named parameters via `.member()`
-syntax for the standard CGAL tags (e.g. `geom_traits`, `vertex_point_map`).
-**Package-local tags do not yet have member-function counterparts**, so
+CGAL upstream supports chaining via `.member()` syntax for the standard
+CGAL tags (e.g. `.geom_traits(...).vertex_point_map(...)`), but the
+mechanism requires modifying CGAL's `parameters_interface.h` to register
+new member functions on `Named_function_parameters` — which we
+deliberately treat as a read-only vendored dependency.
+
+Instead, conformallab++ provides a **pipe-operator overload** in
+`namespace CGAL` (so ADL finds it) that achieves the same effect by
+left-to-right composition:
 
 ```cpp
-// DOES NOT COMPILE:
-CGAL::parameters::output_uv_map(uv).normalise_layout(true);
+auto params = CGAL::parameters::gradient_tolerance(1e-12)
+            | CGAL::parameters::max_iterations(500)
+            | CGAL::parameters::output_uv_map(uv);
+CGAL::discrete_conformal_map_euclidean(mesh, params);
 ```
 
-is currently rejected. Pass one parameter per call instead. This is
-the same limitation noted in `test_cgal_phase8b_lite.cpp`:
+Read as: "first apply gradient_tolerance, then max_iterations, then
+output_uv_map".  The result is a `Named_function_parameters` chain
+indistinguishable from what `.gradient_tolerance(...).max_iterations(...)
+.output_uv_map(...)` would have produced, so every entry function in the
+package accepts it as-is.
 
-```cpp
-// Named-parameter chaining (`a.b().c()`) is not currently supported on
-// the package-local tags; pass one parameter per call instead.
-```
+Implementation: see the `operator|` in
+`code/include/CGAL/Conformal_map/internal/parameters.h`.
+Tests: `CGALPhase8bLite.NamedParamPipe_MultipleParamsTakeEffect` +
+`NamedParamPipe_TwoParams`.
 
-Adding member-function chaining is a separate Phase 8b extension —
-requires writing a derived `Named_function_parameters` subclass that
-exposes `.output_uv_map(...)`, `.normalise_layout(...)`, etc.
+The `.member()` chaining of CGAL standard tags continues to work
+unchanged — `|` is added alongside, not replacing.
 
 ---