feat(prime): wire prompt_override into the daily prep prompt

The prime_schedules.prompt_override column existed end-to-end but was
never populated or read. DailyPrepPrompt.BuildPrompt now takes an
optional override and appends it as an extra paragraph after the fixed
prompt (additive, never a replacement, so a user can't disable the
required get_daily_prep_candidates/set_my_day flow). PrimeRunner passes
schedule.PromptOverride through. The Prime tab in Settings now has a
multiline field per schedule wired to a new PromptOverride property on
PrimeScheduleRowViewModel (blank persists as null).

tests/ClaudeDo.Data.Tests/PrimeScheduleRepositoryTests.cs

@@ -0,0 +1,67 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using Microsoft.EntityFrameworkCore;
+
+namespace ClaudeDo.Data.Tests;
+
+public sealed class PrimeScheduleRepositoryTests : IDisposable
+{
+    private readonly string _dbPath;
+    private readonly ClaudeDoDbContext _ctx;
+    private readonly PrimeScheduleRepository _repo;
+
+    public PrimeScheduleRepositoryTests()
+    {
+        _dbPath = Path.Combine(Path.GetTempPath(), $"claudedo_prime_{Guid.NewGuid():N}.db");
+        var options = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={_dbPath}")
+            .Options;
+        _ctx = new ClaudeDoDbContext(options);
+        _ctx.Database.EnsureCreated();
+        _repo = new PrimeScheduleRepository(_ctx);
+    }
+
+    public void Dispose()
+    {
+        _ctx.Dispose();
+        foreach (var suffix in new[] { "", "-wal", "-shm" })
+            try { File.Delete(_dbPath + suffix); } catch { }
+    }
+
+    [Fact]
+    public async Task UpsertAsync_then_GetAsync_roundtrips_the_prompt_override()
+    {
+        var entity = new PrimeScheduleEntity { PromptOverride = "Also prioritize anything tagged #urgent." };
+
+        await _repo.UpsertAsync(entity);
+        var found = await _repo.GetAsync(entity.Id);
+
+        Assert.NotNull(found);
+        Assert.Equal("Also prioritize anything tagged #urgent.", found!.PromptOverride);
+    }
+
+    [Fact]
+    public async Task UpsertAsync_with_null_override_persists_as_null()
+    {
+        var entity = new PrimeScheduleEntity { PromptOverride = null };
+
+        await _repo.UpsertAsync(entity);
+        var found = await _repo.GetAsync(entity.Id);
+
+        Assert.NotNull(found);
+        Assert.Null(found!.PromptOverride);
+    }
+
+    [Fact]
+    public async Task UpsertAsync_updates_the_override_on_an_existing_row()
+    {
+        var entity = new PrimeScheduleEntity { PromptOverride = "old override" };
+        await _repo.UpsertAsync(entity);
+
+        entity.PromptOverride = "new override";
+        await _repo.UpsertAsync(entity);
+
+        var found = await _repo.GetAsync(entity.Id);
+        Assert.Equal("new override", found!.PromptOverride);
+    }
+}