Add configuration option for PR title default source (branch name vs first commit message)

[0xGREG]

Feature Description

Since PR #36606 (merged in 1.26.0), the pull request creation form always uses the first commit's message as the default PR title, even for multi-commit branches. Previously, multi-commit branches would use the branch name as the default title.

While I understand the rationale behind the change (novice users leaving branch names as PR titles), our teams have procedures that make it so branch names automatically meaningful. The new behavior breaks this workflow and requires manually replacing the commit message with the branch name every time.

Proposed Solution

Add a configuration option under [repository.pull-request] in app.ini to let administrators choose the default PR title source. For example:

[repository.pull-request]
;; Options: first-commit, branch-name
DEFAULT_PR_TITLE_SOURCE = first-commit

This would let teams that prefer the old behavior set DEFAULT_PR_TITLE_SOURCE = branch-name, while keeping the new first-commit default for everyone else.

Related info

• Related PR: Use first commit title for multi-commit PRs and fix auto-focus title field #36606
• Related issue: Idea: Don't pre-fill pull request title with branch name #34865
• Gitea version affected: 1.26.0+

[silverwind]

Seems ok to add. This change is deliberatly not compatible to how GitHub does it, so a opt-out can be provided, but the default should stay at first-commit. Ensure proper test coverage when implementing it.

[silverwind]

Note for strict github compat, it would also need to transform/capitalize the branch name. I think it might be good to do that for people prefering strict github compat.