fix(repos create): default new repos to main, not master

`git init` without `-b` inherits the ambient `init.defaultBranch` config,
which is `master` unless the host has configured otherwise, so `pkgmgr
repos create` produced master-based repositories. On top of that, the
push fallback renamed an already-correct `main` branch back to `master`
whenever the initial push failed (missing remote, auth error).

`init()` now requires an explicit `initial_branch` and runs
`git init -b <branch>`; the bootstrapper passes `main` and no longer
falls back to `master` on push failure.

`resolve_base_branch()` keeps its main -> master fallback, since it reads
existing repositories that may legitimately use master.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/pkgmgr/actions/repository/create/git_bootstrap.py

@@ -10,10 +10,12 @@ from pkgmgr.core.git.commands import (
     push_upstream,
 )
 
+DEFAULT_BRANCH = "main"
+
 
 class GitBootstrapper:
     def init_repo(self, repo_dir: str, preview: bool) -> None:
-        init(cwd=repo_dir, preview=preview)
+        init(initial_branch=DEFAULT_BRANCH, cwd=repo_dir, preview=preview)
         add_all(cwd=repo_dir, preview=preview)
         try:
             commit("Initial commit", cwd=repo_dir, preview=preview)
@@ -21,15 +23,8 @@ class GitBootstrapper:
             print(f"[WARN] Initial commit failed (continuing): {exc}")
 
     def push_default_branch(self, repo_dir: str, preview: bool) -> None:
+        branch_move(DEFAULT_BRANCH, cwd=repo_dir, preview=preview)
         try:
-            branch_move("main", cwd=repo_dir, preview=preview)
-            push_upstream("origin", "main", cwd=repo_dir, preview=preview)
-            return
-        except GitPushUpstreamError:
-            pass
-
-        try:
-            branch_move("master", cwd=repo_dir, preview=preview)
-            push_upstream("origin", "master", cwd=repo_dir, preview=preview)
+            push_upstream("origin", DEFAULT_BRANCH, cwd=repo_dir, preview=preview)
         except GitPushUpstreamError as exc:
             print(f"[WARN] Push failed: {exc}")

src/pkgmgr/core/git/commands/init.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ..errors import GitRunError, GitCommandError
+from ..errors import GitCommandError, GitRunError
 from ..run import run
 
 
@@ -8,14 +8,17 @@ class GitInitError(GitCommandError):
     """Raised when `git init` fails."""
 
 
-def init(*, cwd: str = ".", preview: bool = False) -> None:
+def init(*, initial_branch: str, cwd: str = ".", preview: bool = False) -> None:
     """
-    Initialize a repository.
+    Initialize a repository with an explicit initial branch.
 
     Equivalent to:
-      git init
+      git init -b <initial_branch>
+
+    initial_branch: required, so the branch never depends on the ambient
+      `init.defaultBranch` git config (which is `master` unless configured).
     """
     try:
-        run(["init"], cwd=cwd, preview=preview)
+        run(["init", "-b", initial_branch], cwd=cwd, preview=preview)
     except GitRunError as exc:
         raise GitInitError("Failed to initialize git repository.", cwd=cwd) from exc