M2 audit: excise managed connectors and xAI media-gen tools

Managed connectors (grok.com MCP admin) removed root-and-branch:
- The managed-MCP fetch/injection pipeline is gone, including the whole
  kigi-shell-session-support crate (managed-config fetch client, gateway
  tool catalog + dispatch, header injection, refresh task), reactive
  managed re-auth, mcp_doctor's grok.com-source discovery, and the
  [managed_mcps] config surface.
- TUI: the 'Managed by grok.com' section, connectors URL/deep-link,
  Action::OpenManagedConnectors, and session_team_id are gone. Local MCP
  management (list/toggle/add/remove/auth/tools) is fully intact.
- Kept as LOCAL policy: managed-settings.json MCP allow/deny enforcement,
  the multi-source local MCP merge, folder-trust gating. PluginOrigin
  Project/User labels kept (they tag locally discovered plugin dirs).

imagine/media-gen tools (xAI image/video generation) removed:
- image_gen, image_edit, video_gen, image_to_video, reference_to_video
  implementations, registrations, ToolKind/ToolInput/Output variants
  (serde-safe), config plumbing end to end, ZDR video machinery,
  /imagine + /imagine-video commands and guidance text, the bundled
  imagine skill (added to legacy cleanup so user installs delete it),
  and the media-gen render path.
- Kept: image INPUT (paste/attach, [Image #N] meta, pdf/image fetch,
  clipboard wrap), generic media-ref rendering, and the generic tool
  401-retry machinery (tests renamed, assertions unweakened).
- deploy_app stays: it is a permanently-disabled local stub deploying
  nowhere.

121 files changed, 8 deleted. Gates: workspace check/clippy 0/0, fmt,
deny ok; suites green (tools 2554, shell 4862, tui 6608, workspace
1042). Remaining grok.com strings live only in the auth-method ids and
changelog archives (§9/M3 sweep).

Cargo.lock

@@ -6293,7 +6293,6 @@ dependencies = [
  "kigi-sandbox",
  "kigi-shared",
  "kigi-shell-base",
- "kigi-shell-session-support",
  "kigi-sqlite-journal",
  "kigi-subagent-resolution",
  "kigi-system-power",
@@ -6389,27 +6388,6 @@ dependencies = [
  "windows 0.61.3",
 ]
 
-[[package]]
-name = "kigi-shell-session-support"
-version = "0.1.0"
-dependencies = [
- "agent-client-protocol",
- "axum",
- "chrono",
- "kigi-file-utils",
- "kigi-http",
- "kigi-shell-base",
- "kigi-version",
- "kigi-workspace",
- "reqwest 0.12.28",
- "serde",
- "serde_json",
- "thiserror 2.0.18",
- "tokio",
- "tokio-util",
- "tracing",
-]
-
 [[package]]
 name = "kigi-sqlite-journal"
 version = "0.1.0"