chore: cut v1.9.15 — h2 multiplexing + block QUIC + UI a11y + GitHub Actions full tunnel docs

Wraps four already-merged PRs into a release:
- PR #799 (@dazzling-no-more): HTTP/2 multiplexing on the relay leg with idempotency-safe h1 fallback. ALPN-negotiates h2; one TCP/TLS connection multiplexes ~100 streams instead of the pool. Slow Apps Script calls no longer head-of-line-block the queue on the same socket. force_http1 kill switch in config. 180→197 tests (+17).
- PR #805 (@yyoyoian-pixel): block_quic default true. QUIC over the TCP-based tunnel was TCP-over-TCP meltdown; browsers fall back to TCP/HTTPS within seconds when UDP/443 is dropped. Adds Android + desktop UI toggles.
- PR #819 (@brightening-eyes): enabled accesskit on eframe so screen readers (NVDA/JAWS/VoiceOver/Orca) can navigate the desktop UI. Closes #750.
- PR #783 (@euvel): GitHub Actions Full tunnel docs + workflow YAML files for users who can't buy a VPS. cloudflared Quick / ngrok / cloudflared Named.

Strategically: h2 multiplexing is the architectural fix for #781 / #773 perceived-slowness regression — it makes the pool tuning machinery much less load-bearing. force_http1 kill switch is there if anything goes sideways in the wild.

Tests: 197 lib + 35 tunnel-node green. UI release-mode build green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mhrv-rs"
-version = "1.9.14"
+version = "1.9.15"
 edition = "2021"
 description = "Rust port of MasterHttpRelayVPN -- DPI bypass via Google Apps Script relay with domain fronting"
 license = "MIT"