Backlog: Extended Element slash commands catalog

[mjkatgithub]

Planning

• Milestone: Backlog (unassigned)
• Priority: P3
• Size: XL
• Estimate: 5+ SP (split when picked up)

Goal

Backlog catalog of additional Element slash commands to implement after
the framework (#110) and high-value message commands ship.

Each row may become its own issue when scheduled.

Command catalog (Element Web, develop)

Messages & formatting

• /plain — send without markdown rendering
• /html — send raw HTML body
• /me — emote message
• /msg — send to user/room alias
• /rainbow, /rainbowme — rainbow text

Profile & room metadata

• /nick, /myroomnick
• /myavatar, /myroomavatar, /roomavatar
• /roomname, /topic

Moderation & membership

• /invite, /part, /ban, /unban, /remove
• /ignore, /unignore, /whois

Utility / power-user

• /upgraderoom, /jumptodate, /converttodm, /converttoroom
• /rageshake, /devtools, /verify, /discardsession
• /addwidget, /query, /help

Notes

• Many moderation commands need existing PL/permission UX — may overlap
  room/space settings work.
• /plain and /html need editor/serialize alignment (Element has edge cases).
• Do not start this issue wholesale — split into focused issues per cluster.

Epic

Sub-issue of #109.