docs: add Git commit resource guide

assets/code_example/docs/plugins/resources/gitcommit/updatecli.yaml

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+scms:
+  application:
+    kind: git
+    spec:
+      branch: main
+      url: https://github.com/example/application.git
+
+sources:
+  from-scm:
+    name: Get the latest commit from the configured SCM
+    kind: gitcommit
+    scmid: application
+    spec:
+      branch: main
+
+  from-url:
+    name: Get the latest commit from a Git URL
+    kind: gitcommit
+    spec:
+      branch: main
+      depth: 1
+      url: https://github.com/example/application.git
+
+  from-path:
+    name: Get the latest commit from a local repository
+    kind: gitcommit
+    spec:
+      path: ./application
+
+conditions:
+  exists-in-scm:
+    name: Check that the source commit exists in the configured SCM
+    kind: gitcommit
+    scmid: application
+    sourceid: from-scm
+
+  pinned-commit:
+    name: Check that a pinned commit exists in the repository
+    kind: gitcommit
+    disablesourceinput: true
+    spec:
+      url: https://github.com/example/application.git
+      hash: 69619610a3fac402931709dfbe89d113041c8776

content/en/docs/plugins/resource/gitCommit.adoc

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+---
+title: "Git Commit"
+description: "Retrieve the latest commit hash from a Git branch"
+lead: "kind: gitcommit"
+date: 2026-07-16T09:30:00+07:00
+draft: false
+images: []
+menu:
+  docs:
+    parent: "plugin-resource"
+toc: true
+plugins:
+  - source
+  - condition
+---
+// <!-- Required for asciidoctor -->
+:toc:
+// Set toclevels to be at least your hugo [markup.tableOfContents.endLevel] config key
+:toclevels: 4
+
+[cols="1^,1^,1^",options=header]
+|===
+| source | condition | target
+| &#10004; | &#10004; | &#10008;
+|===
+
+The Git Commit "source" returns the latest commit hash referenced by a Git branch.
+
+The Git Commit "condition" checks that a commit exists in a repository.
+The commit hash defaults to the source output and can be overridden with `spec.hash`.
+Abbreviated hashes are supported.
+
+The target stage is not supported because commit hashes are immutable values.
+
+== Repository selection
+
+Both the source and the condition select a repository in the following order:
+
+. The repository configured by `spec.url` is cloned.
+. Otherwise, `spec.path` selects an existing local repository.
+. Otherwise, the working directory from `scmid` is used.
+
+When `spec.branch` is omitted, the current `HEAD` commit is returned.
+When it is set, Updatecli resolves the local branch first and then its `origin` remote-tracking branch.
+The lookup does not check out the branch or modify the working tree.
+
+== Parameters
+
+{{< resourceparameters "sources" "gitcommit" >}}
+
+[NOTE]
+====
+YAML parses an unquoted all-digit value as a number.
+Quote `spec.hash` when the commit hash only contains digits.
+====
+
+== Example
+
+The following manifest shows SCM, URL, and local-path inputs.
+
+[source,yaml]
+----
+# updatecli.yaml
+{{<include "assets/code_example/docs/plugins/resources/gitcommit/updatecli.yaml">}}
+----