Core Rule Set: Mastodon's ordinary requests pass by default (closes #238)

Adds mastodon.conf, the twelfth change. On Mastodon's paths, the fields
that carry a search, a name, a title, an address or free text skip the four
rules that read them as commands or system files. These cover the API, the
admin and settings pages, sign-in, and the objects other servers deliver to
an inbox. A post's text skips 932125, 932230 and 932235 too. Uploaded file
names skip 932180, and an ActivityPub Accept header skips 920600 on account
paths. Only Mastodon's own resources under /api/v1/ and /admin/ count, since
gitea and Drupal serve those prefixes. The requests recorded from Mastodon
4.7.5 pass at the defaults and while bodies are read.

Model: opus-5-5

README.md

@@ -581,22 +581,24 @@ 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
+- `smallwebwaf` changes the Core Rule Set in twelve ways so that ordinary
+  requests get through to a code forge, to WordPress, to Drupal, to MediaWiki
+  and to Mastodon. 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
-  [`SPEC.md`](SPEC.md) lists them.
+  wikitext do. On Mastodon's own paths, its searches, names, posts and
+  deliveries from other servers do. 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.
+    - MediaWiki;
+    - Mastodon.
 - `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