docs: fix quickstart drift, add LICENSE, document admin bypass and LDAPS cert mount for public release (#17)

Cleanup pass ahead of the public release announcement:

- docs/index.md: fix the Quick Start block, which described a stale
  "edit config then re-run setup.sh a second time" flow. setup.sh now
  requires setup.env (with CFG_BASE_DN) before it will do anything, and
  builds + bootstraps + starts in a single run. Updated to match
  README.md's correct 4-line sequence.
- Add a standard MIT LICENSE at the repo root (theta42, 2026) so
  docs/index.md's "MIT License — see the repository for details" claim
  is actually true.
- docs/standalone.md: document the hardcoded auth.adminUsers:
  ['proxyadmin2'] local anti-lockout admin bypass written into every
  generated proxy-secrets.js — what it's for, that it requires a
  matching SSO user to actually use, and how to rename/extend/disable
  it.
- README.md + docker-compose.yml: fix the LDAPS strict-trust security
  note, which implied mounting the SSO's cert into the proxy was a
  config-only change. It also requires a docker-compose.yml edit
  (ldap-certs isn't mounted into the proxy service); added commented-out
  boilerplate for that mount and clarified the doc text.
- Also includes the pre-existing "Why use this instead of running the
  two separately?" README paragraph that was already staged as
  in-progress work.
- Verified: no Vagrant references, no emoji, and no hardcoded
  custom-domain URLs anywhere in this repo outside the proxy/ and
  sso-manager-node/ submodules; no docs/CNAME (github.io URL scheme
  confirmed).
- Added --- section dividers to docs/*.md to match README.md's
  formatting convention.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 theta42
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.