Add LDAP and Active Directory authentication with secure POST login handling.

The Sync Plugin Info workflow ran on pushes to both `dev` and `main`
while always using the same `chore/sync-info` branch. A `dev` run
force-pushed that branch onto `dev`, so the `main` sync PR (#330)
suddenly showed the whole LDAP connector, and two bot PRs (#330, #331)
shared one branch. Separately, `sync-info.sh` iterated i18n files in
unsorted `find` order, so `zh_CN`/`en_US` could swap between runs and
produce large reorder-only diffs.

Changes:
- Trigger only on pushes to `dev` (changes reach `main` via dev); set
`base: dev` explicitly and `delete-branch: true`.
- Add a `concurrency` group so back-to-back pushes don't race on the
branch.
- Sort i18n files with `LC_ALL=C sort` so key order is deterministic
(`en_US`, then `zh_CN`, matching the current file).

Tested locally on `dev`: the regenerated `plugins_desc.json` only adds
the new LDAP and vector-search entries (+65/−0), with no reordering, and
two runs are byte-identical.

Co-authored-by: robinv8 <robinv8@users.noreply.github.com>