feat(config): add commitMessageGenerator config for external commit message generation

Add a new `git.commitMessageGenerator` configuration option that allows
users to specify a shell command to generate commit messages from staged
changes (e.g. using AI tools). The command should call `git diff
--cached` itself and output a commit message where the first line is
the title and the rest after a blank line is the body.

Also extract the "Generating commit message..." subtitle string into
the translation set for localization support, and update the JSON
schema to include the new configuration definition.

docs-master/Config.md

@@ -481,6 +481,13 @@ git:
   # to 40 to disable truncation.
   truncateCopiedCommitHashesTo: 12
 
+  # Config for external commit message generation (e.g. AI)
+  commitMessageGenerator:
+    # Shell command to generate a commit message from staged changes.
+    # The command should call `git diff --cached` itself and output a
+    # commit message (first line = title, rest after blank line = body).
+    command: ""
+
 # Periodic update checks
 update:
   # One of: 'prompt' (default) | 'background' | 'never'

pkg/gui/controllers/helpers/commits_helper.go

@@ -253,7 +253,7 @@ func (self *CommitsHelper) addCoAuthor(suggestionFunc func(string) []*types.Sugg
 
 func (self *CommitsHelper) generateCommitMessageAsync(command string) {
 	origSubtitle := self.c.Views().CommitDescription.Subtitle
-	self.c.Views().CommitDescription.Subtitle = "Generating commit message..."
+	self.c.Views().CommitDescription.Subtitle = self.c.Tr.GeneratingCommitMessage
 
 	// Snapshot current content so we can detect user edits
 	origSummary := self.getCommitSummary()

pkg/i18n/english.go

@@ -331,6 +331,7 @@ type TranslationSet struct {
 	CommitSummaryTitle                    string
 	CommitDescriptionTitle                string
 	CommitDescriptionSubTitle             string
+	GeneratingCommitMessage               string
 	CommitDescriptionFooter               string
 	CommitDescriptionFooterTwoBindings    string
 	CommitHooksDisabledSubTitle           string
@@ -1434,6 +1435,7 @@ func EnglishTranslationSet() *TranslationSet {
 		CommitSummaryTitle:                   "Commit summary",
 		CommitDescriptionTitle:               "Commit description",
 		CommitDescriptionSubTitle:            "Press {{.togglePanelKeyBinding}} to toggle focus, {{.commitMenuKeybinding}} to open menu",
+		GeneratingCommitMessage:              "Generating commit message...",
 		CommitDescriptionFooter:              "Press {{.confirmInEditorKeybinding}} to submit",
 		CommitDescriptionFooterTwoBindings:   "Press {{.confirmInEditorKeybinding1}} or {{.confirmInEditorKeybinding2}} to submit",
 		CommitHooksDisabledSubTitle:          "(hooks disabled)",

schema-master/config.json

@@ -37,6 +37,17 @@
       "type": "object",
       "description": "Config relating to the commit length indicator"
     },
+    "CommitMessageGeneratorConfig": {
+      "properties": {
+        "command": {
+          "type": "string",
+          "description": "Shell command to generate a commit message from staged changes.\nThe command should call `git diff --cached` itself and output a\ncommit message (first line = title, rest after blank line = body)."
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "description": "Config for external commit message generation (e.g. AI)"
+    },
     "CommitPrefixConfig": {
       "properties": {
         "pattern": {
@@ -446,6 +457,10 @@
           "type": "integer",
           "description": "When copying commit hashes to the clipboard, truncate them to this length. Set to 40 to disable truncation.",
           "default": 12
+        },
+        "commitMessageGenerator": {
+          "$ref": "#/$defs/CommitMessageGeneratorConfig",
+          "description": "Config for external commit message generation (e.g. AI)"
         }
       },
       "additionalProperties": false,