fix(dm): Remove DM button from messages and filter only CLI contacts

Two improvements to DM functionality:

1. Removed DM button from message blocks in channel view
   - Users should use the DM page directly instead
   - Cleaner UI without redundant buttons

2. Filter only CLI (client) contacts in DM dropdown
   - Added filter_types parameter to parse_contacts()
   - get_contacts_list() now returns only CLI contacts
   - Repeaters (REP), rooms (ROOM), and sensors (SENS) are excluded
   - You can't send DMs to repeaters anyway!

Updated README.md to reflect these changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

app/static/js/app.js

@@ -347,9 +347,6 @@ function createMessageElement(msg) {
                 <button class="btn btn-outline-secondary btn-sm btn-reply" onclick="replyTo('${escapeHtml(msg.sender)}')">
                     <i class="bi bi-reply"></i> Reply
                 </button>
-                <button class="btn btn-outline-secondary btn-sm btn-reply" onclick="startDmTo('${escapeHtml(msg.sender)}')">
-                    <i class="bi bi-envelope"></i> DM
-                </button>
             </div>
         ` : ''}
     `;