Fix flexible-wish double-booking, extend calendar cache to 2055, add journey tests

Second real bug found by driving the running app while the suites were green.

Flexible wishes were funded twice across propose -> apply -> re-propose. Because
planned_leave_day carries no wish_id, the engine could not tell that applied days
were that wish's own prior occurrence; it treated them as occupied space, routed
the candidate search around them, and funded the year again on shifted dates while
reporting weeks_funded 1.0. Applying twice turned "one week each spring" into 18
paid days instead of 9. Fixed wishes were unaffected and stay unaffected.

Fix (allocation_service.py), per the approved approach of counting already-applied
days inside the bounding range rather than adding a wish_id column:
- _Ledger._persisted_lookup snapshots existing days BEFORE this run folds in its
  own freshly-computed windows, so a fixed wish's new placement is never mistaken
  for a flexible wish's history
- _reuse_already_funded_window finds this wish's persisted dates within its bound
  and reuses the window containing them, via the ordinary fund_window path
- full funding therefore yields zero new days and partial funding tops up exactly
  the remainder, with no duplication and no false shortfall
- with no persisted dates, or if the reused window is no longer collision-free, it
  falls through to the original search, so an unsatisfied year is never frozen

Calendar cache extended 2026-2035 -> 2026-2055 (39KB -> 116KB) and the allocator
switched to strict, so an uncached year raises UncachedYearError -> ValidationError
-> HTTP 422 instead of silently treating Julafton, Nyarsafton and Midsommarafton as
working days. Also fixed normalize_day dropping the second name when two holidays
share a date (Nationaldagen was being lost). 2049 and 2055 legitimately have 17 red
days, not 18: Pingstdagen coincides with Nationaldagen.

New backend/tests/integration/test_user_journey.py drives the real app over HTTP
across seven journeys: the double-booking guard, the fixed-wish control, apply
idempotency, fixed-never-displaced-by-flexible, flexible wishes tracking Easter
per year, age-4 arithmetic self-consistency, and a recursive check that no Swedish
text reaches the wire now that everything is message_key + data.

New backend/scripts/seed_demo.py seeds a realistic workspace through the real
service layer for manual testing: demo@example.com / DemoPass123!

Backend 414 -> 435 tests. Frontend unchanged at 705.

Still not verified in a browser.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RXMhc9nT6sNz1SL4j8dznL

backend/tests/unit/test_holidays.py

@@ -194,11 +194,11 @@ class TestKlamdag:
         assert not is_klamdag(datetime.date(2027, 3, 2))
 
     def test_klamdag_detected_for_uncached_fallback_year(self) -> None:
-        """2040 is outside the cached range (2026-2035): 2040-04-30 (Mon) is
-        squeezed between Sunday 4/29 and Första maj (Tue 5/1). `is_klamdag`
-        is computed generically from `is_non_working_day`, so this works even
-        without cached klämdag data for the year."""
-        assert is_klamdag(datetime.date(2040, 4, 30))
+        """2060 is outside the cached range (2026-2055): 2060-01-02 (Fri) is
+        squeezed between Nyårsdagen (Thu 1/1) and the weekend (Sat 1/3).
+        `is_klamdag` is computed generically from `is_non_working_day`, so
+        this works even without cached klämdag data for the year."""
+        assert is_klamdag(datetime.date(2060, 1, 2))
 
 
 # ---------------------------------------------------------------------------
@@ -234,29 +234,29 @@ class TestGetRedDays:
 
 
 # ---------------------------------------------------------------------------
-# Fallback path for years outside the cached range (2026-2035)
+# Fallback path for years outside the cached range (2026-2055)
 # ---------------------------------------------------------------------------
 
 
 class TestFallbackForUncachedYear:
     def test_uncached_year_still_returns_formal_holidays(self) -> None:
-        """2040 is outside the cache -> falls back to the `holidays` library:
+        """2060 is outside the cache -> falls back to the `holidays` library:
         formal röda dagar are still known."""
-        result = get_swedish_holidays(2040)
-        assert datetime.date(2040, 12, 25) in result  # Juldagen
-        assert datetime.date(2040, 1, 1) in result  # Nyårsdagen (+ Söndag combo)
+        result = get_swedish_holidays(2060)
+        assert datetime.date(2060, 12, 25) in result  # Juldagen
+        assert datetime.date(2060, 1, 1) in result  # Nyårsdagen (+ Söndag combo)
 
     def test_uncached_year_does_not_know_de_facto_days(self) -> None:
         """Documents the fallback's known limitation: no de facto-day data
         exists outside the cached range, so julafton is NOT marked free."""
-        assert not is_non_working_day(datetime.date(2040, 12, 24))
+        assert not is_non_working_day(datetime.date(2060, 12, 24))
 
     def test_uncached_year_easter_sunday_survives_sondag_filter(self) -> None:
         """The exact-match trap applies to the fallback path too."""
-        red_days = get_red_days(2040)
-        # Easter 2040: verified against `holidays.Sweden(years=2040)`.
+        red_days = get_red_days(2060)
+        # Easter 2060: verified against `holidays.Sweden(years=2060)`.
         easter_sunday = next(
-            d for d, name in get_swedish_holidays(2040).items() if "Påskdagen" in name
+            d for d, name in get_swedish_holidays(2060).items() if "Påskdagen" in name
         )
         assert easter_sunday in red_days