Serve video and poster previews for invite links (#9306)

Invite links currently return HTML without preview metadata. Add
server-rendered `og:video` and `og:image` tags for `/invite/<code>`, and
bundle the approved MP4 and wordmark-only poster from #9282 into the
relay image. Media URLs use the request’s resolved community host, with
only TLS posture from `RELAY_URL`. Unknown hosts and lookup failures
receive no metadata; previews stay generic and never redeem invites.

Validation: production web build, workspace Clippy, 52 router tests
(including real HTTP and MP4 range requests), metadata tests, and
independent agent review pass. `just ci` stops at unrelated mobile
dependency/format checks. The full relay suite was attempted but stopped
during database-dependent tests without local infrastructure. Broad
local Rust/desktop hooks were stopped for disk pressure; desktop/mobile
hooks also lack dependencies and were skipped to publish this draft.
Full-stack and native Messages playback remain unverified. The new
preview regressions run in both CI test-runner paths.

Rollout: merge and deploy the resulting relay image with its web bundle,
verify the invite HTML and both public media URLs, then share a fresh
invite in Messages. Full-stack and human validation remain outstanding.

---------

Signed-off-by: kenny lopez <klopez4212@gmail.com>
Co-authored-by: Terp <5856f6900e8e0a4e0ea1f4f8d2ee33e4753d2119bc122f94ecafc660b46c0511@buzz.block.builderlab.xyz>

scripts/run-tests.sh

@@ -532,6 +532,9 @@ run_unit_tests() {
   run_test_step "buzz-relay binary tests" \
     cargo test -p buzz-relay --bin buzz-relay -- --nocapture
 
+  run_test_step "buzz-relay public invite previews" \
+    cargo test -p buzz-relay --lib invite_preview -- --nocapture
+
   run_test_step "buzz-relay invitation token and cutoff contracts" \
     cargo test -p buzz-relay --lib invite_token:: -- --nocapture
   run_test_step "buzz-relay invitation cutoff configuration" \