remove experimental web UI

The web UI shipped as "experimental" and was never finished — no nav
off the dashboard, no live updates, no settled design, never a
supported surface. It was opt-in by default already; leaving the code
in the tree for v0.1.0 only invited "does this work?" questions and
kept HostSummary/BangerSummary/SudoStatus types on the public RPC
surface that nothing else uses.

Removed:

  internal/webui/                         (all Go + templates + assets)
  internal/daemon/web.go                  (server start / Layout / Config / ListVMs / ListImages)
  internal/daemon/dashboard.go            (DashboardSummary aggregator)

Simplified:

  internal/api/types.go                   drop WebURL on PingResult, drop
                                          HostSummary / SudoStatus / BangerSummary /
                                          DashboardSummary / DashboardSummaryResult
  internal/model/types.go                 drop DaemonConfig.WebListenAddr
  internal/config/config.go               drop web_listen_addr from fileConfig + Load
  internal/daemon/daemon.go               drop webListener / webServer / webURL fields +
                                          startWebServer() call + ping WebURL population
  internal/cli/banger.go                  `daemon status` output no longer branches on web
  internal/daemon/{doc.go,ARCHITECTURE.md} drop web UI sections
  README.md                               drop web_listen_addr config bullet + security paragraph

Tests updated to reflect the new shape. Coverage 57.3 -> 58.9% (the
webui package was largely untested; its removal lifts the ratio
without moving the numerator). `banger daemon status` output and
--help are web-free. Lint + full suite green.

internal/api/types.go

@@ -11,7 +11,6 @@ type Empty struct{}
 type PingResult struct {
 	Status  string `json:"status"`
 	PID     int    `json:"pid"`
-	WebURL  string `json:"web_url,omitempty"`
 	Version string `json:"version,omitempty"`
 	Commit  string `json:"commit,omitempty"`
 	BuiltAt string `json:"built_at,omitempty"`
@@ -298,42 +297,3 @@ type KernelCatalogEntry struct {
 type KernelCatalogResult struct {
 	Entries []KernelCatalogEntry `json:"entries"`
 }
-
-type SudoStatus struct {
-	Available bool   `json:"available"`
-	Command   string `json:"command,omitempty"`
-	Error     string `json:"error,omitempty"`
-}
-
-type HostSummary struct {
-	CPUCount                  int   `json:"cpu_count"`
-	TotalMemoryBytes          int64 `json:"total_memory_bytes"`
-	StateFilesystemTotalBytes int64 `json:"state_filesystem_total_bytes"`
-	StateFilesystemFreeBytes  int64 `json:"state_filesystem_free_bytes"`
-}
-
-type BangerSummary struct {
-	ImageCount             int     `json:"image_count"`
-	ManagedImageCount      int     `json:"managed_image_count"`
-	VMCount                int     `json:"vm_count"`
-	RunningVMCount         int     `json:"running_vm_count"`
-	ConfiguredVCPUCount    int     `json:"configured_vcpu_count"`
-	ConfiguredMemoryBytes  int64   `json:"configured_memory_bytes"`
-	ConfiguredDiskBytes    int64   `json:"configured_disk_bytes"`
-	UsedSystemOverlayBytes int64   `json:"used_system_overlay_bytes"`
-	UsedWorkDiskBytes      int64   `json:"used_work_disk_bytes"`
-	RunningCPUPercent      float64 `json:"running_cpu_percent"`
-	RunningRSSBytes        int64   `json:"running_rss_bytes"`
-	RunningVSZBytes        int64   `json:"running_vsz_bytes"`
-}
-
-type DashboardSummary struct {
-	GeneratedAt time.Time     `json:"generated_at"`
-	Host        HostSummary   `json:"host"`
-	Sudo        SudoStatus    `json:"sudo"`
-	Banger      BangerSummary `json:"banger"`
-}
-
-type DashboardSummaryResult struct {
-	Summary DashboardSummary `json:"summary"`
-}