fix: edge-control: deregister has no ownership check — any authorized SSH key can take over any project (#1091)

Require the caller to prove ownership on deregister by providing the
pubkey that was used during registration. The stored pubkey is loaded
from registry.json and compared byte-for-byte against the supplied key.

Changes:
- Add get_pubkey() helper to lib/ports.sh
- Update do_deregister() to verify caller pubkey before removing project
- Update SSH protocol to "deregister <project> <pubkey>"
- Update bin/disinto CLI to read tunnel keypair and pass pubkey
- Return {"error":"pubkey mismatch"} on failure (no pubkey leakage)
- Add unit tests for both success and failure paths

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/edge-control/lib/ports.sh

@@ -187,6 +187,20 @@ list_ports() {
   echo "$registry" | jq -r '.projects | to_entries | map({name: .key, port: .value.port, fqdn: .value.fqdn}) | .[] | @json' 2>/dev/null
 }
 
+# Get the pubkey for a project
+# Usage: get_pubkey <project>
+# Returns: pubkey string or empty
+get_pubkey() {
+  local project="$1"
+
+  _ensure_registry_dir
+
+  local registry
+  registry=$(_registry_read)
+
+  echo "$registry" | jq -r ".projects[\"$project\"].pubkey // empty" 2>/dev/null || echo ""
+}
+
 # Get full project info from registry
 # Usage: get_project_info <project>
 # Returns: JSON object with project details