feat(discord): add gateway channel flow in wasm (#944)

* feat(discord): restore gateway channel flow in wasm

* chore(discord): bump channel version to 0.2.1

* fix(discord): address review feedback on gateway channel PR

- Add #[serde(default)] to DiscordMessageMetadata for backward compat
  with old Option<String> serialized metadata
- Restore mention polling alongside Gateway (on_poll processes gateway
  events first, then runs poll_for_mentions if configured)
- Update on_respond to handle source_message_id with message_reference
  for mention-poll reply threading
- Implement Gateway presence status: dnd before pairing, online after
- Implement Gateway resume (OP 6) with session_id tracking, falling
  back to fresh identify on Invalid Session (OP 9)
- Extract WebsocketSessionState and spawn_websocket_poll to reduce
  nesting in start_websocket_runtime
- Simplify should_apply_dm_pairing tautology
- Remove completed plan docs
- Fix clippy items_after_test_module in extensions handler

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix(discord): address review findings in gateway channel PR

- Fix gateway presence always showing "online" by filtering empty
  owner_id strings from workspace store reads
- Fix interaction followup using POST instead of PATCH to
  /messages/@original, which left deferred "thinking" state unresolved
- Restore mention-poll pagination (up to 5 pages of 100 messages)
- Remove dead ed25519-dalek and hex dependencies from WASM crate
- Remove unused _channel_id parameter from remember_processed_id
- Clean up redundant let binding in send_pairing_reply

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix(discord): address second-round review findings

- Log warning when gateway event queue JSON fails to deserialize
  instead of silently returning empty (zmanian review item 1)
- Defer presence update from OP 10 Hello to after OP 0 READY, per
  Discord gateway protocol which requires READY before non-Identify
  commands (zmanian review item 2)
- Add 0-25% random jitter to websocket reconnect backoff per Discord's
  reconnection recommendations (zmanian suggestion)
- Extract WebsocketPollContext struct to replace 19-parameter
  spawn_websocket_poll function (zmanian suggestion)
- Document intent bitmask 4609 = GUILDS + GUILD_MESSAGES +
  DIRECT_MESSAGES in capabilities JSON (zmanian suggestion)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

---------

Co-authored-by: zhyaoyu <[email protected]>
Co-authored-by: [email protected] <[email protected]>
Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

Cargo.toml

@@ -40,6 +40,7 @@ eula = false
 tokio = { version = "1", features = ["full"] }
 tokio-stream = { version = "0.1", features = ["sync"] }
 futures = "0.3"
+tokio-tungstenite = { version = "0.26", features = ["rustls-tls-native-roots"] }
 eventsource-stream = "0.2"
 
 # HTTP client
@@ -201,7 +202,6 @@ zbus = "4"
 [dev-dependencies]
 tokio-test = "0.4"
 tracing-test = "0.2"
-tokio-tungstenite = "0.26"
 testcontainers-modules = { version = "0.11", features = ["postgres"] }
 pretty_assertions = "1"
 tempfile = "3"