GeezerVison

Choosing a skill from the `/` menu now inserts a skill chip into the
composer instead of `/alias` text, and the message sends it as a
structured `skill-invocation` part (#30861), so chatd loads that exact
skill's body into the prompt.

- A Lexical `SkillInvocationNode` renders the chip with a remove button;
`/clear` and `/compact` still insert as commands, and typed `/name` text
that wasn't picked from the menu still goes out as plain text (#31126
turns a typed full alias into a chip).
- `buildChatInputContent` emits text and skill parts in document order,
a chip-only message can be sent, drafts keep chips, and the new chat
form forwards them.
- `insertSkill(source, name)` on the composer handle inserts a chip at
the caret without duplicating one that's already there. The project
action bar later in this stack uses it.
- Arrow keys step over chips instead of selecting them. Selecting a chip
node dropped the browser selection, so the next keystroke landed at the
start of the message; file reference chips had the same bug and get the
same fix.
- Copy and paste keep chips: copied text includes `/source/name`,
pasting skips a chip that's already in the composer, and a chip for a
skill this chat can't use is pasted as plain text.

Rendering the parts in the transcript and edit flow is in the next PR.

Dogfood UAT passed on this stack: picking project, personal and
organization skills sends one skill part each and the agent answers from
the skill body without calling `read_skill`; the caret, paste and copy
cases above, drafts, `/clear`, `/compact` and the 400 for a disabled or
deleted skill all behaved as expected.

| Chip in the composer | Sent message in the transcript |
| --- | --- |
| <img alt="Skill chip in the project composer"
src="https://raw.githubusercontent.com/coder/coder/assets/pr-30880-skill-chips/pr/composer-chip.png"
width="600" /> | <img alt="Skill chip in the sent message with the
codeword reply"
src="https://raw.githubusercontent.com/coder/coder/assets/pr-30880-skill-chips/pr/transcript-chip.png"
width="600" /> |

Stack (merge top to bottom):
- #30826
- #30827
- #30838
- #30840
- #30854
- #30855
- #30856
- #30861
- #30880 👈
- #30881
- #30882
- #30884
- #31122
- #31126

---------

Co-authored-by: Cursor <[email protected]>

Renders `skill-invocation` parts from #30861 in the conversation. A user
message shows its skill chips inline with the text, and a message with
only a skill invocation is no longer treated as empty. Editing a past
message restores its chips in the composer (the editable payload now
carries the serialized editor state), optimistic edits keep skill parts,
and queued messages show the skill.

| Editing a message with a chip | Queued message |
| --- | --- |
| <img alt="Editing a past message restores its skill chip"
src="https://raw.githubusercontent.com/coder/coder/assets/pr-30880-skill-chips/pr/edit-chip.png"
width="600" /> | <img alt="Queued message showing its skill"
src="https://raw.githubusercontent.com/coder/coder/assets/pr-30880-skill-chips/pr/queued-chip.png"
width="600" /> |

Stack (merge top to bottom):
- #30826
- #30827
- #30838
- #30840
- #30854
- #30855
- #30856
- #30861
- #30880
- #30881 👈
- #30882
- #30884
- #31122
- #31126

---------

Co-authored-by: Cursor <[email protected]>
Co-authored-by: Nick Vigilante <[email protected]>