refactor(core): consolidate the fingerprint-pinning verifier into core::tls

Per plan §2.5: the security-critical rustls fingerprint-pinning ServerCertVerifier
was hand-rolled three times — quic/endpoint.rs (PinVerify), pf-client-core
library.rs, punktfunk-tray status.rs — drifting copies on a trust boundary. Add
one canonical punktfunk_core::tls::PinVerify (+ cert_fingerprint) behind a light
`tls` feature (rustls + sha2 only, no QUIC runtime); `quic` now depends on it, and
quic::endpoint re-exports cert_fingerprint so that path stays byte-stable
(gamestream + pf-client-core reach it there).

- core::tls::PinVerify: new(pin) for the HTTP clients, with_observed(pin, slot)
  for the QUIC TOFU connect. Behavior-identical to all three originals (pin-check
  + real CertificateVerify signature verification; only hashes the leaf when a pin
  or observed slot needs it). Two focused unit tests anchor the boundary.
- quic/endpoint.rs: drop the private PinVerify, wire client_pinned through
  tls::PinVerify::with_observed.
- pf-client-core library.rs + tray status.rs: use the shared verifier; tray also
  routes load_pin through core cert_fingerprint and drops its direct sha2 dep,
  gaining only the light core `tls` feature (still no host dep, no QUIC runtime).

Verified on Linux (home-worker-5): clippy 0/0 for core(quic), core(tls),
pf-client-core, tray, host(nvenc,vulkan-encode,pyrowave); core 153 lib tests +
loopback 7/7 (pinned handshake) + c_abi round-trip green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-tray/Cargo.toml

@@ -28,7 +28,11 @@ serde_json = "1"
 # pins the ring provider explicitly anyway).
 ureq = { version = "2", default-features = false, features = ["tls"] }
 rustls = { version = "0.23", default-features = false, features = ["ring", "logging", "std", "tls12"] }
-sha2 = "0.10"
+# The one shared cert-fingerprint pin verifier (`punktfunk_core::tls::PinVerify`) + fingerprint
+# hash, instead of the tray hand-rolling its own copy on a trust boundary. The light `tls` feature
+# is rustls + sha2 only (no QUIC runtime / tokio), so this stays a lean helper; core is a pure-Rust
+# leaf (no C toolchain), unlike the host dependency ruled out above.
+punktfunk-core = { path = "../punktfunk-core", default-features = false, features = ["tls"] }
 
 [target.'cfg(windows)'.dependencies]
 # SCM QUERY_STATUS works unprivileged — the service-state probe. Same crate the host service uses.