refactor(routes): move memory domain into routes/memory/ subpackage (#5007)

Slice 2c of the route-domain reorganization (#4082/#4071, per
specs/architecture-runtime-inventory.md §6.3). Moves memory_routes.py into
routes/memory/, leaving a backward-compat sys.modules shim at the old path.
Pure file reorganization, no behavior change.

The shim uses sys.modules replacement (same pattern as the merged gallery
#4903 and research #4975 slices) so that `import routes.memory_routes`,
`from routes.memory_routes import X`, `importlib.import_module(...)`, and
the `import ... as mr` + `monkeypatch.setattr(mr, ...)` pattern used by
test_memory_routes_session_owner.py / test_memory_owner_isolation.py all
operate on the same module object the application uses.

The canonical module does NOT depend on the shim — routes/memory/
memory_routes.py imports only from services/, core/, src/, and stdlib (zero
internal routes/ coupling).

Four source-introspection test sites repointed to the new canonical path:
- test_direct_upload_limits.py
- test_upload_limits_centralized.py (two dict keys)
- test_vision_owner_scope.py

Adds tests/test_memory_routes_shim.py to pin the sys.modules shim contract
(legacy and canonical paths resolve to the same module object; monkeypatch
via legacy alias reaches the canonical module).

Verified: compileall clean; full suite 4219 passed, 3 skipped.

tests/test_upload_limits_centralized.py

@@ -84,7 +84,7 @@ def test_routes_import_from_upload_limits_not_local_defs():
             'int(os.getenv("ODYSSEUS_GALLERY_UPLOAD_MAX_BYTES"',
             'int(os.getenv("ODYSSEUS_GALLERY_TRANSFORM_UPLOAD_MAX_BYTES"',
         ],
-        "routes/memory_routes.py": ['int(os.getenv("ODYSSEUS_MEMORY_IMPORT_MAX_BYTES"'],
+        "routes/memory/memory_routes.py": ['int(os.getenv("ODYSSEUS_MEMORY_IMPORT_MAX_BYTES"'],
         "routes/personal_routes.py": ['os.getenv("ODYSSEUS_PERSONAL_UPLOAD_MAX_BYTES"'],
         "routes/email_routes.py": ["EMAIL_COMPOSE_UPLOAD_MAX_BYTES = 25 * 1024 * 1024"],
         "routes/stt_routes.py": ["STT_MAX_AUDIO_BYTES = 25 * 1024 * 1024"],
@@ -98,7 +98,7 @@ def test_routes_import_from_upload_limits_not_local_defs():
     # And each imports from upload_limits.
     imports = {
         "routes/gallery/gallery_routes.py": "GALLERY_UPLOAD_MAX_BYTES",
-        "routes/memory_routes.py": "MEMORY_IMPORT_MAX_BYTES",
+        "routes/memory/memory_routes.py": "MEMORY_IMPORT_MAX_BYTES",
         "routes/personal_routes.py": "PERSONAL_UPLOAD_MAX_BYTES",
         "routes/email_routes.py": "EMAIL_COMPOSE_UPLOAD_MAX_BYTES",
         "routes/stt_routes.py": "STT_MAX_AUDIO_BYTES",