chat: Slack-level composer markup + fix clipped inline toolbar (F-385/F-386)

[th3-br41n]

What

Two user-reported chat issues (screenshot: selecting text popped a broken clipped shard of a toolbar; no way to write lists in a message), fixed at the shared <CompactEditor> level so chat, comments and the Agent composer all inherit it.

Fix — clipped/stacked selection toolbar (F-385)

The toolbar borrows the fancy-menus .fm-menu glass, which ships flex-direction: column; overflow: hidden. editor-theme.css pinned row/visible at equal specificity (0,1,0), so whichever stylesheet an app's bundle emits last wins — Notes happened to order them safely, chat didn't, and the toolbar painted as a clipped vertical stack. Now the order-proof compound .fm-menu.notes__inline-toolbar (0,2,0) — the exact pattern the toolbar's own colour/overflow dropdowns already carried for the same reason.

Feature — Slack composer vocabulary (F-386)

• Blocks: bulleted / numbered / to-do lists, quote, code block (ListNode/ListItemNode/QuoteNode/CodeNode + ListPlugin/CheckListPlugin).
• Markdown shortcuts: - · 1. · [] · > · fenced code · inline marks · [text](url) — deliberately no headings (a message is not a document).
• Enter semantics: Enter sends (unchanged); Shift+Enter is a soft newline, or the next list item when the caret is in a list (Slack model).
• Toolbar: opt-in bullet/numbered/to-do toggles on the shared InlineToolbarPlugin (lists prop, on for every CompactEditor; Notes/full editors unchanged).
• Autolink: typed/pasted bare URLs link as you type; www. hosts get https:// prepended.
• Read path: baseline theme + compact-editor.css carry the checklist face; the Lexical-free renderEditorState now renders check lists with checked state, so sent messages match the draft. Inline @-mentions already rendered in-text (PR feat(mentions): Slack-style inline @-mentions in chat + agent composers, avatar circle fix #74).

Verification

• packages/editor 589 tests green (new: composer node round-trip, curated markdown vocabulary incl. no-headings, Enter-submit vs Shift+Enter-next-item); apps/chat 39 green; apps/agent green; typecheck + lint (incl. css-token check) clean.
• New real-shell visual spec tests/visual/specs/chat-rich-composer.spec.ts: asserts the toolbar's computed horizontal geometry (regression for the cascade bug), toolbar list toggle, Shift+Enter next item, and [ ] / 1. send round-trips.

toolbar (was a clipped 2-button stack)	sent lists
horizontal B/I/U/S/code + list toggles + colour/link pill	bullets, unchecked to-do, numbered — rendered in transcript

Friction log F-385/F-386 + the implementation-plan Chats-slice rung land in the docs repo alongside this.

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