feat: custom branch name templates (#571)

* Add branch-name-template config option

* Logging

* Use branch name template

* Add label to template variables

* Add description template variable

* More concise description for branch_name_template

* Remove more granular time template variables

* Only fetch first label

* Add check for empty template-generated name

* Clean up comments, docstrings

* Merge createBranchTemplateVariables into generateBranchName

* Still replace undefined values

* Fall back to default on duplicate branch

* Parameterize description wordcount

* Remove some over-explanatory comments

* NUM_DESCRIPTION_WORDS: 3 -> 5

action.yml

@@ -23,6 +23,10 @@ inputs:
     description: "The prefix to use for Claude branches (defaults to 'claude/', use 'claude-' for dash format)"
     required: false
     default: "claude/"
+  branch_name_template:
+    description: "Template for branch naming. Available variables: {{prefix}}, {{entityType}}, {{entityNumber}}, {{timestamp}}, {{sha}}, {{label}}, {{description}}. {{label}} will be first label from the issue/PR, or {{entityType}} as a fallback. {{description}} will be the first 5 words of the issue/PR title in kebab-case. Default: '{{prefix}}{{entityType}}-{{entityNumber}}-{{timestamp}}'"
+    required: false
+    default: ""
   allowed_bots:
     description: "Comma-separated list of allowed bot usernames, or '*' to allow all bots. Empty string (default) allows no bots."
     required: false
@@ -178,6 +182,7 @@ runs:
         LABEL_TRIGGER: ${{ inputs.label_trigger }}
         BASE_BRANCH: ${{ inputs.base_branch }}
         BRANCH_PREFIX: ${{ inputs.branch_prefix }}
+        BRANCH_NAME_TEMPLATE: ${{ inputs.branch_name_template }}
         OVERRIDE_GITHUB_TOKEN: ${{ inputs.github_token }}
         ALLOWED_BOTS: ${{ inputs.allowed_bots }}
         ALLOWED_NON_WRITE_USERS: ${{ inputs.allowed_non_write_users }}