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_test.go

@@ -202,23 +202,6 @@ feed_url = "https://e.com/rss"
 tier = 1
 poll_interval_minutes = 20
 enabled = true
-`},
-		{"direct_route not in channels", `
-[matrix]
-homeserver = "https://h"
-user_id = "@p:h"
-password = "pw"
-[matrix.channels]
-tech = "!t:e"
-[storage]
-db_path = "/tmp/t.db"
-[[sources]]
-name = "S"
-feed_url = "https://e.com/rss"
-tier = 1
-poll_interval_minutes = 20
-direct_route = "gaming"
-enabled = true
 `},
 	}