docs(messaging): unified team reaction vocabulary (#89)

Reconciles the Common Reaction Patterns table with the team semantics
the operator defined on 2026-08-13 (the it-maintenance skill's lifecycle
reference now carries the identical table — this PR keeps the two skills
from contradicting each other):

- **👍** meant *acknowledged/receipt* here — receipts are **🤖** (agent
read-receipt); 👍 is agreement ("I'm in")
- **⏳** meant *in progress* — active work is **▶️** with the
retire-on-stop lifecycle (redact the reaction when work stops); ⏳ is
re-scoped to *waiting/queued*
- **👀** scoped to *looking, no commitment* (was "started investigating")
- adds **▶️ ↩️ 💡 🤖 👎**

Counterpart: it-maintenance-skill MR !95 (internal).

Author: CybotTM

skills/matrix-communication/references/messaging-guide.md

@@ -48,14 +48,22 @@ uv run skills/matrix-communication/scripts/matrix-react.py "#dev:matrix.org" '$e
 
 ### Common Reaction Patterns
 
+Unified team vocabulary (2026-08-13). Downstream copies of this table exist —
+when changing semantics here, keep them in sync:
+
 | Emoji | Meaning | Use Case |
 |-------|---------|----------|
+| ▶️ | Actively working NOW | Set on the claim message; REDACT it when work stops — a lingering ▶️ reads as "still busy" |
 | ✅ | Done/Complete | Mark task as finished |
-| 👍 | Acknowledged | Confirm receipt |
-| 👀 | Looking into it | Started investigating |
+| ⏳ | Waiting/queued | Nobody actively on it (NOT "in progress" — that is ▶️) |
 | 🚀 | Deployed/Shipped | Indicate release |
-| ⏳ | In progress | Working on it |
-| ❌ | Failed/Blocked | Indicate problem |
+| ❌ | Attempt failed | Distinct from 👎 (declining) and ↩️ (questions) |
+| 👀 | Looking at it | No commitment to work on it |
+| ↩️ | Back to reporter | Went back with questions |
+| 💡 | Helpful | This message taught me something |
+| 🤖 | Agent read-receipt | The agent read it and tries to heed it |
+| 👍 | Agreement, I'm in | NOT a receipt acknowledgement (that is 🤖) |
+| 👎 | Count me out | Rather not |
 
 **Workflow example:** Send "Going to reboot server" then later add checkmark reaction when complete.