feat: use hq- prefix for Mayor and Deacon session names

Town-level services (Mayor, Deacon) now use hq- prefix instead of gt-:
- hq-mayor (was gt-mayor)
- hq-deacon (was gt-deacon)

This distinguishes town-level sessions from rig-level sessions which
continue to use gt- prefix (gt-gastown-witness, gt-gastown-crew-max, etc).

Changes:
- session.MayorSessionName() returns "hq-mayor"
- session.DeaconSessionName() returns "hq-deacon"
- ParseSessionName() handles both hq- and gt- prefixes
- categorizeSession() handles both prefixes
- categorizeSessions() accepts both prefixes
- Updated all tests and documentation

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

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

internal/cmd/nudge_test.go

@@ -5,10 +5,10 @@ import (
 )
 
 func TestResolveNudgePattern(t *testing.T) {
-	// Create test agent sessions (no Town field for mayor/deacon anymore)
+	// Create test agent sessions (mayor/deacon use hq- prefix)
 	agents := []*AgentSession{
-		{Name: "gt-mayor", Type: AgentMayor},
-		{Name: "gt-deacon", Type: AgentDeacon},
+		{Name: "hq-mayor", Type: AgentMayor},
+		{Name: "hq-deacon", Type: AgentDeacon},
 		{Name: "gt-gastown-witness", Type: AgentWitness, Rig: "gastown"},
 		{Name: "gt-gastown-refinery", Type: AgentRefinery, Rig: "gastown"},
 		{Name: "gt-gastown-crew-max", Type: AgentCrew, Rig: "gastown", AgentName: "max"},
@@ -27,12 +27,12 @@ func TestResolveNudgePattern(t *testing.T) {
 		{
 			name:     "mayor special case",
 			pattern:  "mayor",
-			expected: []string{"gt-mayor"},
+			expected: []string{"hq-mayor"},
 		},
 		{
 			name:     "deacon special case",
 			pattern:  "deacon",
-			expected: []string{"gt-deacon"},
+			expected: []string{"hq-deacon"},
 		},
 		{
 			name:     "specific witness",