Add demo seed data and API fallback for portfolio mode (#27)

## Summary

- **Seed script** (`migrations/seed.sql`): 5 demo players at varied
skill levels (Elite→Casual), full lifetime stats with mode breakdowns,
and 125 matches with realistic placements/K-D/gulag results
- **DB fallback** (`internal/service/player.go`): `SearchPlayer` and
`GetPlayerStats` now fall back to the database when the CoD API is
unavailable, serving seeded data transparently
- **Demo banner** (`web/src/App.vue`): Dismissible warning alert
explaining data is generated (persists per session via sessionStorage)
- **Demo player links** (`web/src/views/HomeView.vue`): Clickable
buttons on the home page for all 5 demo players so visitors know what to
search

### Context

The Activision stats API (`papi-client`) was fully shut down in April
2024. This change converts the app into a portfolio-ready demo that
showcases the full stack without requiring a live API.

## Test plan

- [ ] Run `psql $DATABASE_URL -f migrations/seed.sql` to seed the
database
- [ ] `go build ./...` and `go vet ./...` pass
- [ ] `cd web && npm run build-only && npm run type-check` pass
- [ ] Click any demo player on HomeView — verify redirect to PlayerView
with stats
- [ ] Verify stats cards, charts, and match history table populate
correctly
- [ ] Verify the demo banner appears and can be dismissed
- [ ] Search for a non-existent player — verify "Player not found" error

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: grovecj

internal/service/player.go

@@ -29,6 +29,7 @@ func NewPlayerService(codClient codclient.CodClient, playerRepo *repository.Play
 }
 
 // SearchPlayer verifies a player exists via the CoD API, persists them, and returns search results.
+// Falls back to database if the API is unavailable.
 func (s *PlayerService) SearchPlayer(ctx context.Context, platform, gamertag, title, mode string) (*PlayerSearchResult, error) {
 	if title == "" {
 		title = "mw"
@@ -39,7 +40,8 @@ func (s *PlayerService) SearchPlayer(ctx context.Context, platform, gamertag, ti
 
 	stats, err := s.codClient.GetPlayerStats(ctx, platform, gamertag, title, mode)
 	if err != nil {
-		return nil, err
+		slog.Warn("cod api unavailable, falling back to database", "error", err)
+		return s.searchFromDB(ctx, platform, gamertag, mode)
 	}
 
 	player, err := s.playerRepo.Upsert(ctx, platform, gamertag)
@@ -64,6 +66,7 @@ func (s *PlayerService) SearchPlayer(ctx context.Context, platform, gamertag, ti
 }
 
 // GetPlayerStats fetches player stats from the CoD API, upserts the player, and saves a snapshot.
+// Falls back to database if the API is unavailable.
 func (s *PlayerService) GetPlayerStats(ctx context.Context, platform, gamertag, title, mode string) (*codclient.PlayerStats, error) {
 	if title == "" {
 		title = "mw"
@@ -74,7 +77,8 @@ func (s *PlayerService) GetPlayerStats(ctx context.Context, platform, gamertag,
 
 	stats, err := s.codClient.GetPlayerStats(ctx, platform, gamertag, title, mode)
 	if err != nil {
-		return nil, err
+		slog.Warn("cod api unavailable for stats, falling back to database", "error", err)
+		return s.getStatsFromDB(ctx, platform, gamertag, mode)
 	}
 
 	player, err := s.playerRepo.Upsert(ctx, platform, gamertag)
@@ -92,3 +96,57 @@ func (s *PlayerService) GetPlayerStats(ctx context.Context, platform, gamertag,
 
 	return stats, nil
 }
+
+// searchFromDB looks up a player and their latest stats from the database.
+func (s *PlayerService) searchFromDB(ctx context.Context, platform, gamertag, mode string) (*PlayerSearchResult, error) {
+	player, err := s.playerRepo.GetByPlatformAndTag(ctx, platform, gamertag)
+	if err != nil {
+		return nil, err
+	}
+	if player == nil {
+		return nil, codclient.ErrPlayerNotFound
+	}
+
+	stats, err := s.getStatsFromDB(ctx, platform, gamertag, mode)
+	if err != nil {
+		return nil, err
+	}
+
+	return &PlayerSearchResult{
+		PlayerID: player.ID,
+		Platform: platform,
+		Gamertag: gamertag,
+		Stats:    stats,
+	}, nil
+}
+
+// getStatsFromDB loads the latest stats snapshot for a player from the database.
+func (s *PlayerService) getStatsFromDB(ctx context.Context, platform, gamertag, mode string) (*codclient.PlayerStats, error) {
+	player, err := s.playerRepo.GetByPlatformAndTag(ctx, platform, gamertag)
+	if err != nil {
+		return nil, err
+	}
+	if player == nil {
+		return nil, codclient.ErrPlayerNotFound
+	}
+
+	statsData, _, err := s.playerRepo.GetLatestStats(ctx, player.ID, mode)
+	if err != nil {
+		return nil, err
+	}
+	if statsData == nil {
+		return nil, codclient.ErrPlayerNotFound
+	}
+
+	// statsData is any (from pgx JSONB scan) — round-trip through JSON to decode
+	jsonBytes, err := json.Marshal(statsData)
+	if err != nil {
+		return nil, err
+	}
+	var stats codclient.PlayerStats
+	if err := json.Unmarshal(jsonBytes, &stats); err != nil {
+		return nil, err
+	}
+
+	return &stats, nil
+}