Disable telnet in generated configs; mount templates volume

- Add "no ip telnet" to generated switch configs for security
- Bind-mount templates/ into the container (read-only) so template
  edits take effect without a rebuild, matching config.py/configs/

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CLfUJoQTaUePx1m1d2v2j9

templates/index.html

@@ -1045,6 +1045,7 @@ function buildConfig(sw, c) {
     `sntp server ip-address 10.202.0.16`,
     `ip http secure-server`,
     `ip http secure-redirect`,
+    `no ip telnet`,
     `aggregation mode smac dmac ip port`,
     `spanning-tree mst name ${mac} revision 0`,
     `poe management mode allocation-consumption`,