docs: a front door, and one page on how the pieces relate

The wiki had no entry point worth the name. Its Home page was hardcoded inside
the generator, had drifted into recommending INSTALL-WINDOWS-IIS - the manual
procedure these same docs tell you not to follow for a new site, because it
produces a server the installer then refuses to upgrade - and the page carrying
that warning, llms.txt, was never published at all, because the generator copied
only .md files. The adoption guide had zero inbound links.

START-HERE routes by what a reader came to do: stand up a site, deploy the
shop-floor tools, write a plugin, integrate with the API, understand a decision,
or fix something. It is the shortest correct path per role, not an index - the
sidebar is already the index.

FLEET-ARCHITECTURE is the page nothing else could assume. The server, GE-Enforce,
the asset reporter, the backup collectors and EventSaver were each documented
alone, each assuming a reader who already knew the other four. It draws the
shape, states the rule that explains most of the behaviour - nothing on the
server reaches out to a PC, the fleet asks - and ends with the table that says
which of the five programs to open for a given symptom, since knowing that is
most of the diagnosis.

wikigen renders START-HERE as the landing page rather than a list maintained in
a second place, and publishes llms.txt as LLM-GUIDE.

docs/START-HERE.md

@@ -0,0 +1,64 @@
+# Start here
+
+ShopDB is a per-site asset platform: one instance per plant, plugins for what
+each site tracks. These pages document the server, the plugin contract, and the
+tools that run on shop-floor PCs.
+
+Find yourself below. Each row is the shortest correct path, not everything that
+exists.
+
+## I am standing up ShopDB at a new site
+
+1. [INSTALL-WINDOWS](INSTALL-WINDOWS.md) - one offline installer, start to finish.
+2. [OPERATE-WINDOWS](OPERATE-WINDOWS.md) - restart, logs, backups, upgrades.
+3. [CSV-IMPORT](CSV-IMPORT.md) if the site's data is in spreadsheets, or
+   [IMPORT-API](IMPORT-API.md) if there is a source database to script against.
+
+**Do not** follow INSTALL-WINDOWS-IIS or DEPLOY-WINDOWS-IIS for a new site.
+Those are the manual procedure, kept for hand-built servers that predate the
+installer, and following them produces a server the installer then refuses to
+upgrade.
+
+## I am deploying the shop-floor tools
+
+Read [FLEET-ARCHITECTURE](FLEET-ARCHITECTURE.md) first - it is one page and it
+is what makes the rest make sense.
+
+Then [ADOPTING-AT-ANOTHER-SITE](ADOPTING-AT-ANOTHER-SITE.md), which has worked
+examples for Intune, GE-Enforce and manual installation, and says where each
+artifact comes from.
+
+## I am writing a plugin
+
+1. [PLUGIN-QUICKSTART](PLUGIN-QUICKSTART.md) - scaffold and first run.
+2. [PLUGIN-HOOKS](PLUGIN-HOOKS.md) - the contract. Authoritative.
+3. [PLUGIN-LAB-PRINTEDPARTS](PLUGIN-LAB-PRINTEDPARTS.md) - a real plugin built
+   end to end, to type along with.
+4. [PLUGIN-EXTERNAL-REPO](PLUGIN-EXTERNAL-REPO.md) if it lives in its own
+   repository, and [CONTRACT-STABILITY](CONTRACT-STABILITY.md) before you choose
+   a version pin.
+
+## I am integrating with the API
+
+1. [LLM-GUIDE](LLM-GUIDE.md) (`docs/llms.txt` in the repo, also served at
+   `/api/docs/llms.txt`) - auth, the response envelope, common recipes.
+   Short, and the envelope section is the part people get wrong.
+2. `GET /api/docs` on any running instance - the full spec, browsable.
+3. [API-REFERENCE](API-REFERENCE.md) for prose, [COLLECTOR-INTEGRATION](COLLECTOR-INTEGRATION.md)
+   if you are feeding data in from a PC.
+
+## I am trying to understand why something is built this way
+
+[The ADRs](ADR-001-asset-as-platform-contract.md). They are the decision record,
+they say what was rejected and why, and they are the fastest way to avoid
+relitigating a settled question. [PROJECT-MAP](PROJECT-MAP.md) lists them all
+with their status, along with the current versions and every migration head -
+it is generated, so it is never stale.
+
+## Something is broken
+
+- Server: [OPERATE-WINDOWS](OPERATE-WINDOWS.md), then `shopdb-admin.ps1 check -Json`.
+- A PC or a bay: the symptom table at the end of
+  [FLEET-ARCHITECTURE](FLEET-ARCHITECTURE.md) says which piece to open first.
+- A deploy that half-worked: [UPGRADE](UPGRADE.md) and
+  [BACKUP-RESTORE](BACKUP-RESTORE.md).