Batch route search into two requests and gate old web versions

[MrAlders0n]

Route search now makes at most two requests per search (/routes/search and /routes/cross, both with an optional iatas list) instead of one /routes/cross call per IATA pair. A search over ~372 areas used to fire ~138k requests. Needs beacon-server 2.0.4.

• Scope is the picked areas, else the region's, else global (iatas omitted). Picking every area is global. More than 100 is blocked.
• Hashes are validated (hex, 1–4 bytes) and lowercased.
• Within-area and cross-area results share one table, sorted by hops then last seen.
• A new search, clear or leaving the page aborts in-flight requests. Route search never retries.
• 400 messages from the server are shown as-is, 503 shows a timeout message, and a failed search never says "no routes".

Adds a version gate: the app reads minWebVersion from GET /api/v1/info on load and on tab focus (at most once a minute) and shows a blocking reload screen when it is older. A 404, null or malformed value, or a network error never blocks.

Bumps the version to 2.0.3.