SWW_APPS: an app's Core Rule Set fixes apply only to the hostnames that serve it (closes #220)

Each app's fixes are one .conf file, whose first rule skips the rest
unless Inspect sets tx.app_<name>, and one entry in apps. SWW_APPS names
each hostname's apps. A hostname gets only its apps' fixes; while
SWW_APPS is unset, every hostname gets every app's fixes.

A hostname in SWW_APPS that is not a DNS name, such as *.example.com,
stops the start. Unset, SWW_APPS is logged at start as null; set
empty, as "".

Model: opus-5-5

README.md

@@ -280,6 +280,7 @@ Every setting the code reads, with its default:
 | `SWW_WAF_EXEMPT_PATHS`                   | empty                                                                                    | Path prefixes the Core Rule Set does not inspect.                                                                                                                                                                                                               |
 | `SWW_WAF_BODY_LIMIT`                     | `off`                                                                                    | How much of a request body the Core Rule Set reads, a size up to `64K`; `off` reads none.                                                                                                                                                                       |
 | `SWW_CORE_RULE_SET_EXCLUSIONS_FILE`      | unset                                                                                    | A file of Core Rule Set exclusions, as Coraza directives, that switch rules off for some fields or paths only.                                                                                                                                                  |
+| `SWW_APPS`                               | unset                                                                                    | The apps each hostname serves, `drupal`, `gitea`, `mediawiki` or `wordpress`, such as `git.example.com:gitea;blog.example.com:wordpress`; only those apps' fixes apply there. Unset, every app's fixes apply to every hostname.                                 |
 | `SWW_BLOCKLIST_URLS`                     | empty                                                                                    | Blocklists to fetch, text files of addresses and netblocks one to a line, such as `https://www.spamhaus.org/drop/drop.txt`.                                                                                                                                     |
 | `SWW_BLOCKLIST_REFRESH`                  | `24h`                                                                                    | How long after a list was last tried it is fetched again, `1h` or more.                                                                                                                                                                                         |
 | `SWW_BLOCKLIST_ACTION`                   | `deny`                                                                                   | What a client on a blocklist gets: `deny`, `limit:<percent>` of every limit, or `log`.                                                                                                                                                                          |
@@ -581,22 +582,24 @@ client's limits by tag. See "Request tags" in [`SPEC.md`](SPEC.md).
   headers of every request, and no body unless `SWW_WAF_BODY_LIMIT` is set. In
   front of a code forge, bodies carry what people write and publish, which the
   rules take for attacks.
-- `smallwebwaf` changes the Core Rule Set in eleven ways so that ordinary
-  requests get through to a code forge, to WordPress, to Drupal and to
-  MediaWiki. They include git over HTTP and sign-in through Git Credential
-  Manager on a code forge, and saving a post from the block editor on WordPress.
-  On gitea's own paths, its searches, file names and branch names get through
-  too. On WordPress's own paths, its searches, names and file names do. On
-  Drupal's own paths, the page to return to, its searches and its names get
-  through too. On MediaWiki's own paths, its searches, page titles, names and
-  wikitext do. No setting undoes the changes; "Attack detection" in
+- `smallwebwaf` changes the Core Rule Set in six ways so that it lets ordinary
+  requests to a code forge through, such as git over HTTP and sign-in through
+  Git Credential Manager. No setting undoes the changes; "Attack detection" in
   [`SPEC.md`](SPEC.md) lists them.
-- These apps work out of the box at the default settings, and their recorded
-  ordinary requests pass the Core Rule Set:
-    - gitea;
-    - WordPress;
-    - Drupal;
-    - MediaWiki.
+- Each supported app also has its own fixes, which let its ordinary requests
+  through. Its recorded ordinary requests pass the Core Rule Set at the default
+  settings. The supported apps, by their names in `SWW_APPS`, are:
+    - `gitea`, whose fixes let its searches, file names and branch names
+      through;
+    - `wordpress`, whose fixes let through its searches, its names, its file
+      names and a post saved from the block editor;
+    - `drupal`, whose fixes let through the page to return to, its searches and
+      its names;
+    - `mediawiki`, whose fixes let through its searches, its page titles, its
+      names and its wikitext.
+- `SWW_APPS` names the apps each hostname serves. A hostname gets only its own
+  apps' fixes, and a hostname it does not list gets none. Unset, every app's
+  fixes apply to every hostname.
 - `SWW_CORE_RULE_SET_EXCLUSIONS_FILE` switches single rules off for an app's own
   fields or paths.
 - Rule files are plain text, one rule to a line, edited by hand and read again