feat: remove task management MCP tools (#28354)

Removes the six task-management tools from the MCP tool surface in
`codersdk/toolsdk`:

- `coder_create_task`
- `coder_delete_task`
- `coder_list_tasks`
- `coder_get_task_status`
- `coder_send_task_input`
- `coder_get_task_logs`

Both the coderd-hosted MCP server (`coderd/mcp`) and the CLI `coder exp
mcp server` derive their tool list from `toolsdk.All`, so removing the
registry entries removes the tools from both servers with no server-side
changes.

The MCP server documentation (`docs/ai-coder/mcp-server.md`) is updated
to drop the task-management entry from the tool overview.

## What stays

- `coder_report_task` is intentionally kept: it is the agent-side
status-reporting mechanism (`WithTaskReporter`), already excluded from
the hosted MCP server, and required by `coder exp mcp server`, Claude
Code configuration, and scaletest.
- The `codersdk` Task SDK methods (`CreateTask`, `DeleteTask`, `Tasks`,
`TaskLogs`, etc.) and the Tasks feature (CLI, UI, API) are untouched;
this PR only removes MCP tool registration.
- The task-only `taskIDDescription` helper is deleted; `userDescription`
stays (used by `coder_create_workspace`).

The code change is deletion-only: 970 removed lines across `toolsdk.go`
and its test file, no added behavior.

## Validation

- `go build ./...`, `go test ./coderd/mcp/`, and targeted
`golangci-lint` pass. `go test ./codersdk/toolsdk/` passes all tests;
the package-level goleak failure (agentssh goroutines) reproduces
identically on unmodified `main` and is unrelated to this diff.
- `pnpm run lint-docs` passes on the docs change.
- Remote dogfood UAT ran against the toolsdk change and passed:
`tools/list` on both the hosted MCP endpoint and `coder exp mcp server`
confirms the six tools are absent and the remaining surface is intact
(34 hosted tools; CLI adds `search`/`fetch`), a `tools/call` of
`coder_get_authenticated_user` succeeds, and calling a removed tool
returns `-32602 unknown tool`. `coder_report_task` still registers in
the CLI server when `CODER_MCP_APP_STATUS_SLUG` is set.
- The failing `Pixel / Review` commit status is unrelated: this PR
contains no `site/` changes, and the same status fails on the last 8
`main` commits including this PR's merge base (`676b9bb06bf`).

> Mux acted on Mike's behalf to create this pull request.

docs/ai-coder/mcp-server.md

@@ -94,8 +94,8 @@ through `2026-07-28`, does not issue `Mcp-Session-Id` headers, and answers
 `GET` and `DELETE` with `405 Method Not Allowed` (there is no standalone
 server-event stream or explicit session termination, both permitted by the
 specification). The server exposes tools only; MCP resources, prompts,
-structured tool output, elicitation, and the MCP Tasks extension (which is
-unrelated to Coder's task tools) are not implemented.
+structured tool output, elicitation, and the MCP Tasks extension are not
+implemented.
 
 ### Prerequisites
 
@@ -198,7 +198,6 @@ The MCP server exposes tools across several areas:
 - **Template operations**: list, inspect, create, and manage templates and versions
 - **File operations**: read, write, and edit files in a workspace
 - **Workspace interaction**: run commands, forward ports, list apps, and read logs
-- **Task management**: create, list, inspect, and control tasks
 - **Coder Agents chats**: create chats, send messages, read transcripts and status, interrupt, archive, and list available models
 - **User and system**: authenticated user details, tar uploads, and task reporting