Fix: pass-by-name shadowing still present in gh_detect_default_branch, gh_repo_default_branch, and gh_infer_repo_from_origin

[codeforester]

Summary

The shadowing fix in #123 (commit d62e8c1) renamed local variables from default_branch to detected_branch / remote_default_branch, which resolved the specific case tested. However, those new names are now the dangerous ones. The pattern repeats across three functions.

Root cause

printf -v "$result_var" writes to the variable named by result_var in the current function's scope. If the caller passes a name that collides with a local variable in the function, printf -v silently writes to the function's local — which disappears on return — leaving the caller's variable unchanged.

Function	Shadowing local(s)
gh_detect_default_branch	detected_branch
gh_repo_default_branch	remote_default_branch, status
gh_infer_repo_from_origin	inferred_repo, remote_url

Reproducer

source lib/bash/std/lib_std.sh
source lib/bash/gh/lib_gh.sh

repo_dir=...  # any repo with a main branch

# Passes: 'branch' does not collide with locals
local branch=""
gh_detect_default_branch "$repo_dir" branch
echo "$branch"   # → "main"

# Silent failure: 'detected_branch' collides with the function's local
local detected_branch=""
gh_detect_default_branch "$repo_dir" detected_branch
echo "$detected_branch"   # → "" (caller variable was never set)

Fix

Rename all private intermediates to __-prefixed names in the three functions, consistent with the pattern used in lib_str.sh and lib_list.sh. For example:

gh_detect_default_branch() {
    local repo_dir="$1"
    local result_var="${2:-}"
    local __gh_detect_branch__=""          # was: detected_branch

    ...
    printf -v "$result_var" '%s' "$__gh_detect_branch__"
}

Add regression tests for detected_branch, remote_default_branch, and inferred_repo as the result variable name (similar to the default_branch tests added in #123).