feat(coderd_chat_system_prompt): manage the deployment-wide chat system prompt

docs/resources/chat_system_prompt.md

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+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "coderd_chat_system_prompt Resource - terraform-provider-coderd"
+subcategory: ""
+description: |-
+  ~> This resource is experimental. Changes are to be expected, and we recommend using it with caution in production environments.
+  The deployment-wide chat system prompt for Coder Agents (Settings → Instructions in the dashboard).
+  This is a deployment-wide singleton. Declare it once; duplicate resources silently overwrite each other.
+  Coder sanitizes the stored prompt (strips invisible Unicode characters, normalizes line endings, collapses runs of blank lines, and trims surrounding whitespace), and this resource compares values the same way, so a trailing newline from file(...) does not cause drift after apply. On the first plan after an import, a configured value that differs from the live one only by sanitization shows a single in-place normalization update and then converges; use trimspace(file(...)) to avoid even that.
+  ~> Warning
+  If a system prompt was configured out of band, terraform import this resource before the first apply. Otherwise Terraform overwrites the live value; a plan-time warning is emitted when this is about to happen.
+  ~> Warning
+  terraform destroy resets the prompt to empty and include_default_system_prompt to true, the defaults of a never-configured deployment. The API has no delete operation for this setting.
+  ~> Warning
+  This resource requires Coder version 2.32.0 https://github.com/coder/coder/releases/tag/v2.32.0 or later, and a token with site-wide owner permissions.
+---
+
+# coderd_chat_system_prompt (Resource)
+
+~> This resource is experimental. Changes are to be expected, and we recommend using it with caution in production environments.
+
+The deployment-wide chat system prompt for Coder Agents (`Settings → Instructions` in the dashboard).
+
+This is a deployment-wide singleton. Declare it once; duplicate resources silently overwrite each other.
+
+Coder sanitizes the stored prompt (strips invisible Unicode characters, normalizes line endings, collapses runs of blank lines, and trims surrounding whitespace), and this resource compares values the same way, so a trailing newline from `file(...)` does not cause drift after apply. On the first plan after an import, a configured value that differs from the live one only by sanitization shows a single in-place normalization update and then converges; use `trimspace(file(...))` to avoid even that.
+
+~> **Warning**
+If a system prompt was configured out of band, `terraform import` this resource before the first apply. Otherwise Terraform overwrites the live value; a plan-time warning is emitted when this is about to happen.
+
+~> **Warning**
+`terraform destroy` resets the prompt to empty and `include_default_system_prompt` to `true`, the defaults of a never-configured deployment. The API has no delete operation for this setting.
+
+~> **Warning**
+This resource requires Coder version [2.32.0](https://github.com/coder/coder/releases/tag/v2.32.0) or later, and a token with site-wide `owner` permissions.
+
+## Example Usage
+
+```terraform
+// Keep the prompt itself in a Markdown file next to the Terraform
+// configuration so it can be reviewed like any other prose.
+resource "coderd_chat_system_prompt" "this" {
+  system_prompt = file("${path.module}/system-prompt.md")
+
+  // Append to Coder's built-in system prompt (the default) rather
+  // than replacing it.
+  include_default_system_prompt = true
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `system_prompt` (String) The custom system prompt text, typically `file("${path.module}/system-prompt.md")`. Limited to 128 KiB after sanitization.
+
+### Optional
+
+- `include_default_system_prompt` (Boolean) Whether the custom prompt is appended to Coder's built-in system prompt (`true`, the default) or replaces it entirely (`false`).
+
+## Import
+
+Import is supported using the following syntax:
+
+The [`terraform import` command](https://developer.hashicorp.com/terraform/cli/commands/import) can be used, for example:
+
+```shell
+# The chat system prompt is a deployment-wide singleton, so the import ID is
+# required by the CLI syntax but otherwise unused.
+terraform import coderd_chat_system_prompt.this chat_system_prompt
+```

examples/resources/coderd_chat_system_prompt/import.sh

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+# The chat system prompt is a deployment-wide singleton, so the import ID is
+# required by the CLI syntax but otherwise unused.
+terraform import coderd_chat_system_prompt.this chat_system_prompt

examples/resources/coderd_chat_system_prompt/resource.tf

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+// Keep the prompt itself in a Markdown file next to the Terraform
+// configuration so it can be reviewed like any other prose.
+resource "coderd_chat_system_prompt" "this" {
+  system_prompt = file("${path.module}/system-prompt.md")
+
+  // Append to Coder's built-in system prompt (the default) rather
+  // than replacing it.
+  include_default_system_prompt = true
+}