Group regression tests by domain (#215)

Move the flat backend/tests/*.py into domain subfolders so the suite
mirrors the code's concerns:
  data/          climate, grading, scoring, grid, places, store
  web/           api, content, homepage, views
  notifications/ notify, digest, discord (+ dm/interactions/link)
  accounts/      api_accounts
  core/          metrics, singleton, dashboard

conftest.py stays at the tests/ root, so its sys.path setup and shared
fixtures still apply to every subfolder. The four tests that derive repo
paths from __file__ get their depth bumped one level to match their new
location. Pytest discovers the subfolders recursively; the CI command
(python -m pytest backend/tests) is unchanged.

Claude-Session: https://claude.ai/code/session_01XXxmNFy9cZ6Gh8Y9thZn62

tests/core/test_dashboard.py

@@ -7,7 +7,7 @@ of polls (the non-leader workers) would cry DOWN for a perfectly healthy notifie
 import importlib.util
 import os
 
-REPO = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+REPO = os.path.dirname(os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
 _spec = importlib.util.spec_from_file_location(
     "dashboard", os.path.join(REPO, "scripts", "dashboard.py"))
 dashboard = importlib.util.module_from_spec(_spec)

tests/web/test_content.py

@@ -374,7 +374,7 @@ def test_measure_conversion_constants_match_the_frontend():
     # Same drift risk as the country list: two hand-maintained copies.
     import os
     import content
-    units_js = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
+    units_js = os.path.join(os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))),
                             os.pardir, "frontend", "units.js")
     with open(units_js, encoding="utf-8") as f:
         src = f.read()
@@ -413,7 +413,7 @@ def test_f_country_list_matches_the_frontend():
     # what a first-time visitor should see.
     import os
     import content
-    units_js = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
+    units_js = os.path.join(os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))),
                             os.pardir, "frontend", "units.js")
     with open(units_js, encoding="utf-8") as f:
         src = f.read()

tests/web/test_homepage.py

@@ -215,7 +215,7 @@ def test_homepage_brand_keeps_the_lockup_styling(client, no_feed):
     assert 'class="site-name"' in html
     assert "<h1 class=\"site-name\"" not in html      # the hero owns the h1
 
-    css = (pathlib.Path(__file__).parents[2] / "frontend" / "style.css").read_text()
+    css = (pathlib.Path(__file__).parents[3] / "frontend" / "style.css").read_text()
     lockup = css.split(".brand h1", 1)[1].split("}", 1)[0]
     assert ".brand .site-name" in lockup, (
         "the .brand h1 lockup rule must also match .brand .site-name"

tests/web/test_views.py

@@ -21,7 +21,7 @@ def test_views_and_migrate_import_without_the_web_stack():
             "assert 'fastapi' not in sys.modules, 'views/migrate pulled in FastAPI'; "
             "assert 'app' not in sys.modules, 'views/migrate imported the web app'; "
             "import places; assert places._load_started is False")
-    backend = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+    backend = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
     subprocess.run([sys.executable, "-c", code], cwd=backend, check=True)