chore: housekeeping — linter & formatter setup

Add .prettierrc.json, .markdownlint.json, .yamllint.yaml, .gitattributes
Run CSharpier, Prettier and markdownlint across the entire codebase.
No logic changes — formatting, using order and line endings only.

SECURITY.md

@@ -2,9 +2,8 @@
 
 ## Reporting a Vulnerability
 
-If you find a security issue in HellionChat, please do not open a
-public Gitea issue. Use one of the private channels below so I can
-investigate and ship a fix before the details go public.
+If you find a security issue in HellionChat, please do not open a public Gitea issue. Use one of the private channels
+below so I can investigate and ship a fix before the details go public.
 
 **Preferred:**
 
@@ -13,8 +12,7 @@ investigate and ship a fix before the details go public.
 | Email      | `kontakt@hellion-media.de` |
 | Discord DM | `@j.j_kazama`              |
 
-For urgent disclosures (active exploitation, user-data exposure) email
-is the fastest path.
+For urgent disclosures (active exploitation, user-data exposure) email is the fastest path.
 
 I respond on weekdays during European business hours.
 
@@ -22,8 +20,7 @@ I respond on weekdays during European business hours.
 
 ### In scope
 
-- Code paths that touch user-controlled input (chat messages, plugin
-  config, file paths the user can influence)
+- Code paths that touch user-controlled input (chat messages, plugin config, file paths the user can influence)
 - The privacy filter in `MessageStore.cs` and the export pipeline
 - The configuration migration logic
 - The `EmoteCache` HTTP client and path handling
@@ -31,21 +28,18 @@ I respond on weekdays during European business hours.
 
 ### Out of scope
 
-- Issues in upstream Chat 2 that HellionChat has not modified — report
-  those at <https://github.com/Infiziert90/ChatTwo/issues>
-- Issues in Dalamud itself — those go to
-  <https://github.com/goatcorp/Dalamud>
+- Issues in upstream Chat 2 that HellionChat has not modified — report those at
+  <https://github.com/Infiziert90/ChatTwo/issues>
+- Issues in Dalamud itself — those go to <https://github.com/goatcorp/Dalamud>
 - Issues in the FFXIV game client
 - Anything that requires the user to install a malicious plugin first
 
 ## Disclosure Window
 
-I aim to ship a fix within 14 days for high-severity issues and within
-30 days for everything else. If a fix needs more time I will say so in
-the private thread.
+I aim to ship a fix within 14 days for high-severity issues and within 30 days for everything else. If a fix needs more
+time I will say so in the private thread.
 
 ## Credits
 
-Everyone who reports a real issue gets listed in the changelog of the
-release that fixes it, unless they prefer to stay anonymous. No bug
-bounty, nothing financial — this is a hobby plugin.
+Everyone who reports a real issue gets listed in the changelog of the release that fixes it, unless they prefer to stay
+anonymous. No bug bounty, nothing financial — this is a hobby plugin.