Add GitHub connection type — repo viewer with org grouping and auto-refresh

New protocol type 'github' for browsing repositories via the GitHub REST API.
Creates a non-terminal panel showing repos grouped by owner/org, sorted by
last commit date (newest first), with search filtering and auto-refresh.

Backend:
- ProtocolGitHub constant and GitHubConfig/GitHubRepo model structs
- New internal/githubclient package (REST API, pagination, token validation)
- Session manager connectGitHub() with periodic refresh goroutine
- API surface: RefreshGitHubRepos() for on-demand refresh
- Token stored via existing credential infrastructure (keychain/vault)

Frontend:
- GitHub tab in profile editor with API URL and token storage fields
- New github.js viewer component (grouped repos, badges, language dots)
- github.css with charcoal-themed repo cards and org headers
- Protocol colour tokens, tab badge, sidebar indicator for GitHub
- Event wiring for session:github:repos and session:github:error
- Cleanup on tab close

Supports GitHub Enterprise via configurable API base URL.

internal/models/defaults.go

@@ -11,6 +11,7 @@ const (
 	DefaultSSHPort    = 22
 	DefaultTelnetPort = 23
 	DefaultRAWPort    = 23
+	DefaultGitHubPort = 443
 )
 
 // Default timeout values (in seconds).
@@ -96,6 +97,14 @@ func NewProfile(protocol Protocol) Profile {
 			Encoding:       "utf-8",
 			PayloadPresets: []PayloadPreset{},
 		}
+	case ProtocolGitHub:
+		p.Port = DefaultGitHubPort
+		p.Host = "github.com"
+		p.GitHub = &GitHubConfig{
+			BaseURL:             "https://api.github.com",
+			SecretMode:          SecretModeSaved,
+			RefreshIntervalSecs: 300,
+		}
 	}
 
 	return p

internal/models/models.go

@@ -11,6 +11,7 @@ const (
 	ProtocolSSH    Protocol = "ssh"
 	ProtocolTelnet Protocol = "telnet"
 	ProtocolRAW    Protocol = "raw"
+	ProtocolGitHub Protocol = "github"
 )
 
 // HostKeyPolicy determines how unknown or changed SSH host keys are handled.
@@ -76,6 +77,9 @@ type Profile struct {
 
 	// RAW-specific configuration
 	RAW *RAWConfig `json:"raw,omitempty"`
+
+	// GitHub-specific configuration
+	GitHub *GitHubConfig `json:"github,omitempty"`
 }
 
 // SSHConfig holds SSH-specific settings for a connection profile.
@@ -132,6 +136,36 @@ type PayloadPreset struct {
 	Format  string `json:"format"`  // text, hex, escaped
 }
 
+// GitHubConfig holds GitHub API-specific settings for a connection profile.
+type GitHubConfig struct {
+	// BaseURL is the GitHub API base (e.g. "https://api.github.com" for
+	// github.com, or "https://github.example.com/api/v3" for GHE).
+	BaseURL string `json:"baseURL"`
+
+	// SecretMode controls how the personal access token is stored.
+	SecretMode SecretMode `json:"secretMode"`
+
+	// RefreshIntervalSecs controls the auto-refresh period in seconds.
+	// Defaults to 300 (5 minutes).
+	RefreshIntervalSecs int `json:"refreshIntervalSecs"`
+}
+
+// GitHubRepo is a single repository returned to the frontend for display.
+type GitHubRepo struct {
+	FullName    string `json:"fullName"`
+	Name        string `json:"name"`
+	Owner       string `json:"owner"`
+	Description string `json:"description"`
+	HTMLURL     string `json:"htmlURL"`
+	Private     bool   `json:"private"`
+	Fork        bool   `json:"fork"`
+	Archived    bool   `json:"archived"`
+	Language    string `json:"language"`
+	Stars       int    `json:"stars"`
+	PushedAt    string `json:"pushedAt"` // ISO 8601
+	UpdatedAt   string `json:"updatedAt"`
+}
+
 // SessionState represents the lifecycle state of a connection session.
 type SessionState string