fix: list every page in the Wiki.js sidebar

[PhilippTheServer]

Closes #5

The sidebar showed only Home. The other seven pages were served correctly and reachable
by URL, but nothing linked to them — so unless you already knew a page's name, you could not
find it.

Wiki.js seeds a static navigation list holding only Home at setup, and the bootstrap never
replaced it.

The fix

bootstrap.py rebuilds the sidebar from the pages that actually exist:

[bootstrap] sidebar rebuilt with 8 entries

Icon	Target	Label
mdi-home	/	OpenTaberna
mdi-rocket-launch-outline	/Getting-Started	Getting Started
mdi-shield-key-outline	/Authorization	Authorization
mdi-api	/API/Architecture	API Architecture
mdi-database-outline	/Database/Architecture	Database Architecture
mdi-truck-outline	/Orders-and-Fulfillment	Orders and Fulfillment
mdi-cog-outline	/Configuration	Configuration
mdi-server	/Deployment	Production Deployment

Ordered for reading rather than alphabetically. Pages outside NAV_ORDER are appended
alphabetically, so a new page appears without anyone maintaining a list — add it to
NAV_ORDER only to place it deliberately.

Navigation mode stays MIXED, so the page browser remains available next to the list.

Why the check missed it

check_wikijs.py asserted each page returns 200 to an anonymous request. That was true —
every page was reachable. Reachable is not the same as discoverable, and the check only
tested the first.

It now also decodes the base64 sidebar payload Wiki.js hands the theme on the page root and
fails when a published page is absent from it.

Against the reported bug — sidebar reset to Home only:

$ python3 tools/check_wikijs.py
Checked 8 pages against http://localhost:3030.

7 problem(s):

  FAIL  'API Architecture' (/API/Architecture) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Authorization' (/Authorization) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Configuration' (/Configuration) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Database Architecture' (/Database/Architecture) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Production Deployment' (/Deployment) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Getting Started' (/Getting-Started) is not in the sidebar — reachable by URL, but nothing links to it
  FAIL  'Orders and Fulfillment' (/Orders-and-Fulfillment) is not in the sidebar — reachable by URL, but nothing links to it

Against this branch, from a clean docker compose down -v && docker compose up -d:

$ docker inspect -f '{{.State.ExitCode}}' opentaberna-wiki-bootstrap-1
0
[bootstrap] sidebar rebuilt with 8 entries
[bootstrap] guests can read without signing in
[bootstrap] ready — open the wiki, no login required

$ python3 tools/check_wikijs.py
Checked 8 pages against http://localhost:3030.
OK — every page is served, listed in the sidebar, and no page asks for a login.

The sidebar was decoded from what an anonymous request receives, not from the admin API,
so this verifies what a reader without an account actually gets.