docs: close round-5 token-exchange follow-ups

- settings.toml.example: drop the stale `enable_token_exchange = false`
  deprecated-alias line (the key was removed from config.py _DEFAULTS).
- configuration-migration-v2.md: add a Quick Reference row + note that
  `ENABLE_TOKEN_EXCHANGE` was removed and is now ignored; use
  `MCP_DEPLOYMENT_MODE=login_flow` instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/configuration-migration-v2.md

@@ -27,8 +27,11 @@ This guide helps you migrate from the old configuration variables to the new con
 |----------|----------|--------|
 | `VECTOR_SYNC_ENABLED` | `ENABLE_SEMANTIC_SEARCH` | Deprecated |
 | `ENABLE_OFFLINE_ACCESS` | `ENABLE_BACKGROUND_OPERATIONS` | Deprecated |
+| `ENABLE_TOKEN_EXCHANGE` | `MCP_DEPLOYMENT_MODE=login_flow` | Removed (now ignored) |
 | N/A (auto-detected) | `MCP_DEPLOYMENT_MODE` | New (optional) |
 
+> **`ENABLE_TOKEN_EXCHANGE` was removed.** The OAuth token-exchange mode was never fully implemented and was retired in the ADR-022/ADR-023 consolidation. The variable is now silently ignored — use `MCP_DEPLOYMENT_MODE=login_flow` for multi-user OAuth.
+
 **Tuning parameters unchanged:**
 - `VECTOR_SYNC_SCAN_INTERVAL` - Keep as-is
 - `VECTOR_SYNC_PROCESSOR_WORKERS` - Keep as-is

settings.toml.example

@@ -48,7 +48,6 @@ enable_background_operations = false
 # Deprecated aliases (declared so env var overrides work)
 vector_sync_enabled = false
 enable_offline_access = false
-enable_token_exchange = false
 
 # --- Token storage ---
 token_encryption_key = "@none"