issue E : Widen test_solver_boundary.py and give the accepted residue an allowlist

[florian-simvia]

Child of the solver boundary umbrella. Closing step. Must land after the
other children, not before: run today against the full module list it produces
roughly 160 hits, which is unusable as a gate.

What the test does today

tests/unit/test_solver_boundary.py reads 6 modules and greps them for 5
tokens:

SOLVER_TOKENS = ("code_saturne", "setup.xml", "run.cfg", "RESU", "MESH")
GENERIC_MODULES = [registry.py, doe.py, cli.py, control.py, web_services.py, fastapi_routes/*]

Two weaknesses

The module list covers 6 files out of 20. Not scanned: runner.py,
execution.py, docker.py, logs.py, probes.py, residuals.py,
template.py, web_support.py, maintenance.py, config.py — precisely the
modules holding the most code_saturne conventions.

The token list is too narrow, which makes the test green on files that
leak. Missing at least: listing, monitoring, profiles, run_solver.log,
performance.log, run_status, saturne, POST, residuals.csv.

Concretely, today: cli.py is in the scanned list, passes, and contains 10
code_saturne literals; fastapi_routes/case_data.py is in the scanned list,
passes, and declares file: str = "listing" and scope: str = "monitoring" as
API defaults.

What to do

1. Extend SOLVER_TOKENS with the words above.
2. Extend GENERIC_MODULES to every module outside csauto/solvers/, ideally
   by globbing so a new module is covered automatically instead of being
   forgotten.
3. Add an explicit allowlist for the residue docs/architecture.md already
   records as deliberate: saturne_bin, --saturne-bin, the TOML keys, and the
   historical HTTP names (/api/resu_dirs, resu_removed). The allowlist
   should be a named constant with a comment pointing at that doc section, so
   the test and the documentation state the same thing.
4. Update docs/architecture.md and docs/adding-a-solver.md: today they say
   all solver knowledge sits behind the adapter, which is not true. After this
   work it will be, and the wording should describe the mechanism/vocabulary
   split explicitly.

Definition of done

• The test scans every generic module, with tokens broad enough to catch the
  leaks listed above.
• The allowlist is short, named, commented, and matches the documentation.
• Adding a module to csauto/ puts it under the gate without anyone
  remembering to register it.