v0.9.1: normalize X/Twitter GraphQL URLs for cache hit rate (issue #16)

User @barzamini pointed out an optimization from the Python community
(originally from seramo_ir): X/Twitter GraphQL URLs look like

  https://x.com/i/api/graphql/{hash}/{op}?variables=...&features=...&fieldToggles=...

The features and fieldToggles params change across sessions and even
within a session, busting our 50 MB response cache on every request to
the same logical query. Stripping everything after 'variables=' lets
identical logical queries collapse into one cache entry, dramatically
reducing quota usage when browsing Twitter through the relay.

Implementation:
  - src/domain_fronter.rs: new normalize_x_graphql_url() helper. Matches
    exactly the Python patch's pattern (host == 'x.com', path starts
    with /i/api/graphql/, query starts with variables=). Truncates at
    the first '&' past the '?'. Applied at the top of relay() so the
    normalized URL feeds BOTH the cache key AND the request sent to
    Apps Script — so we save on Apps Script quota too, not just on
    return-trip bytes.
  - src/config.rs: new opt-in normalize_x_graphql bool (default false).
    Off by default because strict X endpoints may reject trimmed requests;
    user should flip it on and watch for regressions.
  - src/bin/ui.rs: checkbox in the Advanced section,
    'Normalize X/Twitter GraphQL URLs', with tooltip explaining the
    trade-off and crediting the source.
  - Four new unit tests in domain_fronter::tests covering: the happy
    path trim, non-x.com hosts pass through unchanged, non-graphql x.com
    paths pass through unchanged, and idempotency. 48 tests total, all
    green.

Credit: idea by seramo_ir, Python patch at
https://gist.github.com/seramo/0ae9e5d30ac23a73d5eb3bd2710fcd67,
implementation request by @barzamini in issue #16.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mhrv-rs"
-version = "0.9.0"
+version = "0.9.1"
 edition = "2021"
 description = "Rust port of MasterHttpRelayVPN -- DPI bypass via Google Apps Script relay with domain fronting"
 license = "MIT"