refactor: remove !paste command, keep as internal helper

Paste creation is only used internally by the bot for multi-line
output. The create_paste() helper remains importable by other plugins.

docs/USAGE.md

@@ -131,7 +131,6 @@ format = "text"               # Log format: "text" (default) or "json"
 | `!abuse <ip> report <cats> <comment>` | Report IP to AbuseIPDB (admin) |
 | `!vt <hash\|ip\|domain\|url>` | VirusTotal lookup |
 | `!emailcheck <email> [email2 ...]` | SMTP email verification (admin) |
-| `!paste <text>` | Create a paste on FlaskPaste |
 | `!shorten <url>` | Shorten a URL via FlaskPaste |
 
 ### Command Shorthand
@@ -848,24 +847,6 @@ bad@example.com -- SMTP 550 User unknown (mx: mail.example.com)
 - 15-second timeout per connection
 - Max 5 emails per invocation
 
-### `!paste` -- Create Paste
-
-Upload text to FlaskPaste and get a shareable URL.
-
-```
-!paste some long text here
-```
-
-Output format:
-
-```
-https://paste.mymx.me/abc12345
-```
-
-- mTLS client cert skips PoW; falls back to PoW challenge if no cert
-- Content sent as JSON body to FlaskPaste API
-- Raw content available at `<paste_url>/raw`
-
 ### `!shorten` -- Shorten URL
 
 Shorten a URL via FlaskPaste's URL shortener.