docs(link): the guide an integrator reads stopped at protocol 6 (Phase 9a)

The Asset Bridge's docs pass, and the acceptance walk that shaped it (v8.md §16
row 9a, §17.13-14). Phase 9 is three legs now: this one, the edge->main cutover,
and the site.

## INTEGRATION.md had stopped at 6 and contradicted itself

Its §2 said "the current version is 6" above examples already carrying
`X-UOLink-Version: 8`, there was no protocol-7 paragraph, and `assets.` appeared
zero times in 1,306 lines. It is the only document an integrator outside this org
has, so it is carried the whole way: the version block corrected, v7 (the event
plane's command half) and v8 (the asset plane) written, a §5 section for the five
routes, 425/422 in the status table, and a caveat that the asset plane is a
working set rather than a stream.

Protocol 7's absence is the Events workstream's debt rather than this one's, but
it cannot be stepped over on the way to 8.

## The operator-facing half

`UPGRADE_NOTES.md` gains the entry an operator reads when this ships: what
changed, the one required action on a Linux host, and the thing that will not
announce itself -- nothing here happens on a restart, so a patched client keeps
serving the old pictures until somebody presses a button.

`installer/INSTALL.md` gains libgdiplus as a prerequisite row and the `doctor`
row that checks it. The index rows for SPAWN_ATLAS and CLILOCS described the
workflows this protocol deleted; v8.md now has an index row of its own, and v7 is
marked as the released protocol.

## The walk

Wiped every asset row and every imported sprite, then walked it as a new
operator: 1,095 portraits in 3.18 s, 67,496 names in 1.42 s, 313 item pictures in
1.38 s, the atlas over the bridge in ~2.0 s, an Update with no drift answered in
0.99 s. Bestiary portraits are the right animals by eye; the marketplace shows
hued item art with cliloc names.

It found two defects (§17.14) and one cutover hazard: module-uo's `edge` is
behind its `main`, missing #35, so the walk measured 0 of 6,455 spawners carrying
a UniqueId. 9b's row says to sync before merging or the cutover ships a
regression.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016wDDVXWMDz82WqE1i969r4

installer/INSTALL.md

@@ -57,6 +57,7 @@ Only the sidecar is exposed, and only to your website.
 | Outbound HTTPS | To `gitea.whitlocktech.com`, to fetch the bundle and the two artifacts. Nothing inbound is needed, and no Gitea account or git client is required. |
 | The sidecar on the **same host** as the shard | The shard connects to `127.0.0.1:7788`. Splitting them is not supported — the loopback socket *is* the trust boundary for inbound commands. |
 | Admin access to your Runic Gateway site | The last step is pasting four values into Admin → Shard (uo-link). |
+| `libgdiplus` *(Linux hosts only)* | Only needed for **artwork**. ServUO runs under Mono on Linux, and Mono's `System.Drawing` — which the shard uses to decode sprites out of your UO client — is a thin layer over this library. Without it the site's creature portraits and item pictures stay empty; names and the spawn atlas are unaffected. `sudo apt-get install libgdiplus` (or `dnf install libgdiplus`); `doctor` checks for it. **Windows hosts need nothing.** See [`../link/SHARD_PREREQS.md`](../link/SHARD_PREREQS.md). |
 
 **Back up first.** The overlay overwrites `Scripts/Scripts.csproj` (a stock file), and the patch
 tier edits stock sources. A copy of `Scripts/` and `Config/` before you start costs nothing.
@@ -527,10 +528,18 @@ first thing a maintainer will want.
 ✓ Protocol                sidecar 4 = overlay manifest 4
 ✗ Shard connected         no — the shard is running (pid 8123) but has not dialed in
 ✓ Bundle                  2026.08.19 — up to date
+⚠ Imaging (libgdiplus)    not found on this host
+    this shard cannot decode artwork out of its UO client — creature portraits and
+    item pictures will be absent; names and the spawn atlas are unaffected
+    install it: apt-get install libgdiplus  /  dnf install libgdiplus
+    see docs/link/SHARD_PREREQS.md — Windows hosts need nothing
 ✓ Backups                 2026-08-19T09:12:44Z — 3 file(s) replaced by update to bundle 2026.08.19
     3 kept in /etc/runicgateway/backups
 ```
 
+The imaging row appears **on Linux hosts only** — a Windows host ships `System.Drawing` with .NET
+Framework and has nothing to check, so there is no row rather than a row saying "not applicable".
+
 Rows come from asking the installed sidecar (`--version`, `--print-config`) rather than from reading
 `install.json`, so `doctor` reports what the binary would actually do — including which config and
 database file the *service* resolves — rather than what the installer believes it was told. The