chore(backend): repair test suite and bring ruff to green

The suite hadn't run green since the routes refactor:
- test_profile_duplicate_names.py imported the pre-refactor module
  layout and broke collection; now imports backend.services.profiles
- tests/conftest.py puts the repo root and backend dir on sys.path so
  files collect standalone instead of depending on run order
- test_cors.py tested a hand-copied mirror of the origin list that had
  drifted from app.py (missing http://tauri.localhost); it now builds
  the app via the real create_app() factory
- test_progress.py simulated a 1KB download, below the tracker's 1MB
  reporting threshold; simulation raised to 5MB
- slow/timeout markers registered in pyproject

Ruff: ~900 violations auto-fixed (typing modernization, import
sorting, unused imports, whitespace). The remaining rules are baselined
in pyproject.toml with per-rule counts to burn down, plus per-file
carve-outs for deliberate env-before-import ordering. ruff check is
now clean; suite is 134 passed, 2 skipped.

backend/tests/test_personality_samples.py

@@ -32,11 +32,9 @@ import sys
 import time
 from dataclasses import asdict, dataclass, field
 from pathlib import Path
-from typing import Optional
 
 import httpx
 
-
 REPO_ROOT = Path(__file__).resolve().parents[2]
 sys.path.insert(0, str(REPO_ROOT))
 
@@ -126,13 +124,13 @@ class Scorecard:
     refined: str
     latency_ms: int
     length_chars: int = 0
-    prompt_leak: Optional[str] = None
-    refusal: Optional[str] = None
+    prompt_leak: str | None = None
+    refusal: str | None = None
     stage_directions: list[str] = field(default_factory=list)
     flags: list[str] = field(default_factory=list)
 
 
-def first_match(patterns, text: str) -> Optional[str]:
+def first_match(patterns, text: str) -> str | None:
     s = text.lstrip()
     for pat in patterns:
         m = pat.search(s)
@@ -186,7 +184,7 @@ known-shipping Kokoro voice so the throwaway profile satisfies the
 preset-engine validator on creation."""
 
 
-def detect_backend_port(hint: Optional[int]) -> int:
+def detect_backend_port(hint: int | None) -> int:
     candidates: list[int] = []
     if hint is not None:
         candidates.append(hint)