style: fix all golangci-lint issues and format code (refs #17)

Fix 380 lint violations across all Go source files including wsl_v5,
nlreturn, noinlineerr, errcheck, funlen, funcorder, tagliatelle,
perfsprint, modernize, revive, gosec, ireturn, mnd, forcetypeassert,
cyclop, and others.

Key changes:
- Split large handler/command functions into smaller methods
- Extract scan helpers for database queries
- Reorder exported/unexported methods per funcorder
- Add sentinel errors in models package
- Use camelCase JSON tags per tagliatelle defaults
- Add package comments
- Fix .gitignore to not exclude cmd/chat-cli directory

internal/models/auth_token.go

@@ -2,7 +2,6 @@ package models
 
 import (
 	"context"
-	"fmt"
 	"time"
 )
 
@@ -23,5 +22,5 @@ func (t *AuthToken) User(ctx context.Context) (*User, error) {
 		return ul.GetUserByID(ctx, t.UserID)
 	}
 
-	return nil, fmt.Errorf("user lookup not available")
+	return nil, ErrUserLookupNotAvailable
 }

internal/models/channel_member.go

@@ -2,7 +2,6 @@ package models
 
 import (
 	"context"
-	"fmt"
 	"time"
 )
 
@@ -23,7 +22,7 @@ func (cm *ChannelMember) User(ctx context.Context) (*User, error) {
 		return ul.GetUserByID(ctx, cm.UserID)
 	}
 
-	return nil, fmt.Errorf("user lookup not available")
+	return nil, ErrUserLookupNotAvailable
 }
 
 // Channel returns the full Channel for this membership.
@@ -32,5 +31,5 @@ func (cm *ChannelMember) Channel(ctx context.Context) (*Channel, error) {
 		return cl.GetChannelByID(ctx, cm.ChannelID)
 	}
 
-	return nil, fmt.Errorf("channel lookup not available")
+	return nil, ErrChannelLookupNotAvailable
 }

internal/models/model.go

@@ -6,6 +6,7 @@ package models
 import (
 	"context"
 	"database/sql"
+	"errors"
 )
 
 // DB is the interface that models use to query the database.
@@ -24,6 +25,12 @@ type ChannelLookup interface {
 	GetChannelByID(ctx context.Context, id string) (*Channel, error)
 }
 
+// Sentinel errors for model lookup methods.
+var (
+	ErrUserLookupNotAvailable    = errors.New("user lookup not available")
+	ErrChannelLookupNotAvailable = errors.New("channel lookup not available")
+)
+
 // Base is embedded in all model structs to provide database access.
 type Base struct {
 	db DB
@@ -40,7 +47,7 @@ func (b *Base) GetDB() *sql.DB {
 }
 
 // GetUserLookup returns the DB as a UserLookup if it implements the interface.
-func (b *Base) GetUserLookup() UserLookup {
+func (b *Base) GetUserLookup() UserLookup { //nolint:ireturn // interface return is intentional
 	if ul, ok := b.db.(UserLookup); ok {
 		return ul
 	}
@@ -49,7 +56,7 @@ func (b *Base) GetUserLookup() UserLookup {
 }
 
 // GetChannelLookup returns the DB as a ChannelLookup if it implements the interface.
-func (b *Base) GetChannelLookup() ChannelLookup {
+func (b *Base) GetChannelLookup() ChannelLookup { //nolint:ireturn // interface return is intentional
 	if cl, ok := b.db.(ChannelLookup); ok {
 		return cl
 	}

internal/models/session.go

@@ -2,7 +2,6 @@ package models
 
 import (
 	"context"
-	"fmt"
 	"time"
 )
 
@@ -23,5 +22,5 @@ func (s *Session) User(ctx context.Context) (*User, error) {
 		return ul.GetUserByID(ctx, s.UserID)
 	}
 
-	return nil, fmt.Errorf("user lookup not available")
+	return nil, ErrUserLookupNotAvailable
 }