Add full-text search, EU channel theme, and web-only sources

Search: new FTS5-backed SearchStories query, /search JSON endpoint,
client-side overlay (search.js) wired into the layout header. EU
channel gets its own theme color (#003399) across bg/text/border/glow
classes. Sources can now route to non-Matrix channels without
validation error (web-only mode); a warning still flags typos.

internal/config/config.go

@@ -140,7 +140,10 @@ func (c *Config) validate() error {
 			return fmt.Errorf("sources[%d] (%s): direct_route is required for enabled sources", i, s.Name)
 		}
 		if _, ok := c.Matrix.Channels[s.DirectRoute]; !ok {
-			return fmt.Errorf("sources[%d] (%s): direct_route %q is not a configured matrix.channels key", i, s.Name, s.DirectRoute)
+			// Not a Matrix channel — treated as web-only (stories visible in the
+			// UI but never posted). Warn so typos still surface.
+			slog.Warn("source routes to non-Matrix channel (web-only)",
+				"source", s.Name, "direct_route", s.DirectRoute)
 		}
 	}