feat(invites): add use-limited invite links (#3141)

## Summary

- add database-backed v2 invite links with optional maximum-use limits
and atomic final-slot redemption
- preserve v1 invite compatibility while adding
exhausted/expired/invalid client handling across desktop, web, and
mobile
- emit structured claim-outcome logs with community, invite ID, outcome,
maximum uses, and post-claim count

## Verification

- `cargo fmt --all -- --check`
- `cargo test -p buzz-db` (85 passed, 134 Postgres-dependent ignored)
- `cargo clippy -p buzz-db --all-targets -- -D warnings`
- desktop `npm run typecheck`
- push hook: desktop checks/tests, desktop Tauri tests, Rust tests, and
branch-skew passed
- Postgres integration tests were previously reviewed green at the
pre-rebase tree; local rerun on this session was unavailable because
Postgres/Docker were not running
- mobile push-hook check could not start because Flutter is unavailable
locally

---------

Signed-off-by: Kalvin Chau <kalvin@block.xyz>
Signed-off-by: npub1dccv64krpcpse5cmkzfeh998cftungyatw3djt8jwdw6g43f7fyqzzmrf7 <6e30cd56c30e030cd31bb0939b94a7c257c9a09d5ba2d92cf2735da45629f248@buzz.block.builderlab.xyz>
Co-authored-by: npub1c4alndp82zyt9veaklm5d965quss79vlhk9awv7qu5erwhmf42qqlvc25c <c57bf9b4275088b2b33db7f746975407210f159fbd8bd733c0e532375f69aa80@buzz.block.builderlab.xyz>
Co-authored-by: npub122y0pqkertljmedu303rl0aqrj3w8pvu43t6jxm6875lzg6f2pwqegc3xc <5288f082d91aff2de5bc8be23fbfa01ca2e3859cac57a91b7a3fa9f12349505c@buzz.block.builderlab.xyz>
Co-authored-by: npub1dccv64krpcpse5cmkzfeh998cftungyatw3djt8jwdw6g43f7fyqzzmrf7 <6e30cd56c30e030cd31bb0939b94a7c257c9a09d5ba2d92cf2735da45629f248@buzz.block.builderlab.xyz>

.github/workflows/ci.yml

@@ -340,6 +340,7 @@ jobs:
           cargo build --profile ci -p buzz-relay -p git-credential-nostr
           cargo nextest archive \
             --cargo-profile ci \
+            -p buzz-db \
             -p buzz-relay \
             -p buzz-test-client \
             --lib \
@@ -671,11 +672,11 @@ jobs:
           done
           cat /tmp/buzz-relay.log
           exit 1
-      - name: Invite claim security tests
+      - name: Invite security tests
         run: |
           cargo nextest run \
             --archive-file target/ci/backend-integration-tests.tar.zst \
-            -E 'package(buzz-relay) and test(claim_)' \
+            -E '(package(buzz-db) and test(/relay_invite::tests/)) or (package(buzz-relay) and test(/api::invites::tests/))' \
             --run-ignored ignored-only
         env:
           DATABASE_URL: postgres://buzz:${{ env.BUZZ_TEST_POSTGRES_PASSWORD }}@localhost:5432/buzz