feat(vacay): half vacation days (#552) (#1631)

* feat(vacay): support half vacation days (#552)

Log a vacation day as a half day (0.5) as well as a full day and count it
as such against the entitlement. A "Half day" mode joins the calendar
toolbar on desktop and mobile; half days render as a diagonal half-fill in
the day cell, and the used/remaining totals carry the fraction.

Closes #552

* refactor(vacay): half-day as a per-person toggle with a corner badge

The diagonal half-fill collided with the two-person split — one person's
half day looked like two people off. Drop the diagonal: the cell fill keeps
showing who is off, a half day gets a small corner ½ badge, and a hover
tooltip lists who is off on that date and how much (only when a half day is
present). Logging moves from a third mode to a Half-day toggle that applies
to the selected person, on desktop and mobile.

* feat(vacay): mark half days with an orange corner dot

Swap the ½ badge for a small orange dot in the bottom-right corner, mirroring
the blue trip dot — quieter in the grid, and the hover tooltip still spells
out who is on a half day.

* fix(vacay): make the fraction migration idempotent

The crosswalk test replays the migration tail (rewind + re-run), which expects
every later migration to be idempotent. Guard the vacay_entries ADD COLUMN
behind a pragma_table_info check so the second run is a no-op. Also only set
dayVisual's `half` flag when true, so full days keep their exact
{ background, numColor } shape for the mobile day-model unit test.

* style(vacay): nudge the mobile day dots slightly inward

The blue trip dot and orange half-day dot sat right in the cell corner on
mobile; move both a touch toward the centre so they read cleaner.

server/src/db/migrations.ts

@@ -3701,6 +3701,14 @@ function runMigrations(db: Database.Database): void {
       `);
       db.exec('CREATE INDEX IF NOT EXISTS idx_hidden_regions_user ON hidden_regions (user_id);');
     },
+    // Half vacation days (#552): a vacay entry can now count as a full day (1) or
+    // a half day (0.5) toward the entitlement. Existing entries default to a full
+    // day, so the entitlement maths are unchanged for everyone already using vacay.
+    // Guarded so re-running the migration tail (e.g. the crosswalk test) is a no-op.
+    () => {
+      const hasFraction = db.prepare("SELECT 1 FROM pragma_table_info('vacay_entries') WHERE name = 'fraction'").get();
+      if (!hasFraction) db.exec('ALTER TABLE vacay_entries ADD COLUMN fraction REAL NOT NULL DEFAULT 1');
+    },
   ];
 
   if (currentVersion < migrations.length) {