feat: logins list/default, actions run delete, date filters, label update alias

- fgj logins {list,default}: complementary UI to 'fgj auth'. 'list'
  shows all configured hosts (hostname, user, protocol, default flag,
  match_dirs) with --json. 'default [hostname]' gets or sets which
  host wins in resolution when no other signal is present.
  Adds 'Default bool' field to HostConfig; GetHost consults it between
  match_dirs and the codeberg.org fallback. Multiple defaults tolerated
  with a stderr warning; alphabetical-first wins.

- fgj actions run delete: delete a completed workflow run via raw
  DELETE (SDK v0.23.2 has no DeleteRepoActionRun). Fetches run first
  and refuses to delete non-terminal states unless --force; suggests
  'actions run cancel' for those. Confirmation prompt unless --yes.

- pr list / issue list gain --since and --before date filter flags.
  Accepts YYYY-MM-DD, RFC 3339, YYYY-MM-DD HH:MM:SS, and relative
  deltas (7d, 24h, 2w, 1m — months=30 days). Issues use server-side
  filter via ListIssueOption.Since/Before; PRs fall back to client-side
  (SDK lacks Since/Before on ListPullRequestsOptions).

- fgj label update added as alias for 'fgj label edit' (tea-compat).

All changes:
  cmd/logins.go (new, 140 LOC)
  cmd/actions_run_delete.go (new, ~85 LOC)
  cmd/pr.go, cmd/issue.go (+parseDateArg helper, filter wiring)
  cmd/label.go (1-line alias)
  internal/config/config.go (Default field + DefaultHost method)
  CHANGELOG.md
Built in parallel by three sub-agents; plus the label alias done
serially. go build / go vet / go test -race all clean.

internal/config/config.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/spf13/viper"
@@ -20,6 +21,7 @@ type HostConfig struct {
 	User        string   `yaml:"user,omitempty"`
 	GitProtocol string   `yaml:"git_protocol,omitempty"`
 	MatchDirs   []string `yaml:"match_dirs,omitempty"`
+	Default     bool     `yaml:"default,omitempty"`
 	Order       int      `yaml:"-"` // config file order, set at load time
 }
 
@@ -134,7 +136,8 @@ func (c *Config) SaveToPath(path string) error {
 // 3. Environment variable (FGJ_HOST)
 // 4. Auto-detected hostname from git remote
 // 5. match_dirs lookup (longest prefix match)
-// 6. Default to codeberg.org
+// 6. Configured default host (HostConfig.Default == true)
+// 7. Default to codeberg.org
 func (c *Config) GetHost(hostname string, detectedHost string, cwd string) (HostConfig, error) {
 	if hostname == "" {
 		hostname = viper.GetString("hostname")
@@ -152,6 +155,10 @@ func (c *Config) GetHost(hostname string, detectedHost string, cwd string) (Host
 		hostname = c.ResolveHostByPath(cwd)
 	}
 
+	if hostname == "" {
+		hostname = c.DefaultHost()
+	}
+
 	if hostname == "" {
 		hostname = "codeberg.org"
 	}
@@ -164,6 +171,27 @@ func (c *Config) GetHost(hostname string, detectedHost string, cwd string) (Host
 	return host, nil
 }
 
+// DefaultHost returns the hostname of the host marked Default == true.
+// If no host is marked default, returns "". If multiple hosts are marked
+// default (a user-error case), the one that sorts first alphabetically is
+// returned and a warning is printed to stderr.
+func (c *Config) DefaultHost() string {
+	var matches []string
+	for hostname, host := range c.Hosts {
+		if host.Default {
+			matches = append(matches, hostname)
+		}
+	}
+	if len(matches) == 0 {
+		return ""
+	}
+	sort.Strings(matches)
+	if len(matches) > 1 {
+		fmt.Fprintf(os.Stderr, "warning: multiple hosts marked default (%s); using %s\n", strings.Join(matches, ", "), matches[0])
+	}
+	return matches[0]
+}
+
 // ResolveHostByPath finds the host whose match_dirs entry is the longest
 // prefix of cwd. Returns "" if no match is found.
 // Both cwd and match_dirs entries are resolved through filepath.EvalSymlinks