fix: Signal adapter parity pass — integration gaps, clawdbot features, env var simplification

Integration gaps fixed (7 files missing Signal):
- cron/scheduler.py: Signal in platform_map (cron delivery was broken)
- agent/prompt_builder.py: PLATFORM_HINTS for Signal (agent knows it's on Signal)
- toolsets.py: hermes-signal toolset + added to hermes-gateway composite
- hermes_cli/status.py: Signal + Slack in platform status display
- tools/send_message_tool.py: Signal example in target description
- tools/cronjob_tools.py: Signal in delivery option docs + schema
- gateway/channel_directory.py: Signal in session-based channel discovery

Clawdbot parity features added to signal.py:
- Self-message filtering: prevents reply loops by checking sender != account
- SyncMessage filtering: ignores sync envelopes (sent transcripts, read receipts)
- Edit message support: reads dataMessage from editMessage envelope
- Mention rendering: replaces \uFFFC placeholders with @identifier text
- Jitter in SSE reconnection backoff (20% randomization, prevents thundering herd)

Env var simplification (7 → 4):
- Removed SIGNAL_DM_POLICY (DM auth follows standard platform pattern via
  SIGNAL_ALLOWED_USERS + DM pairing, same as Telegram/Discord)
- Removed SIGNAL_GROUP_POLICY (derived from SIGNAL_GROUP_ALLOWED_USERS:
  not set = disabled, set with IDs = allowlist, set with * = open)
- Removed SIGNAL_DEBUG (was setting root logger, removed entirely)
- Remaining: SIGNAL_HTTP_URL, SIGNAL_ACCOUNT (required),
  SIGNAL_ALLOWED_USERS, SIGNAL_GROUP_ALLOWED_USERS (optional)

Updated all docs (website, AGENTS.md, signal.md) to match.

tools/cronjob_tools.py

@@ -102,7 +102,9 @@ def schedule_cronjob(
                  - "local": Save to local files only (~/.hermes/cron/output/)
                  - "telegram": Send to Telegram home channel
                  - "discord": Send to Discord home channel
+                 - "signal": Send to Signal home channel
                  - "telegram:123456": Send to specific chat ID
+                 - "signal:+15551234567": Send to specific Signal number
     
     Returns:
         JSON with job_id, next_run time, and confirmation
@@ -216,7 +218,7 @@ Use for: reminders, periodic checks, scheduled reports, automated maintenance.""
             },
             "deliver": {
                 "type": "string",
-                "description": "Where to send output: 'origin' (back to this chat), 'local' (files only), 'telegram', 'discord', or 'platform:chat_id'"
+                "description": "Where to send output: 'origin' (back to this chat), 'local' (files only), 'telegram', 'discord', 'signal', or 'platform:chat_id'"
             }
         },
         "required": ["prompt", "schedule"]

tools/send_message_tool.py

@@ -33,7 +33,7 @@ SEND_MESSAGE_SCHEMA = {
             },
             "target": {
                 "type": "string",
-                "description": "Delivery target. Format: 'platform' (uses home channel), 'platform:#channel-name', or 'platform:chat_id'. Examples: 'telegram', 'discord:#bot-home', 'slack:#engineering'"
+                "description": "Delivery target. Format: 'platform' (uses home channel), 'platform:#channel-name', or 'platform:chat_id'. Examples: 'telegram', 'discord:#bot-home', 'slack:#engineering', 'signal:+15551234567'"
             },
             "message": {
                 "type": "string",