Audited the AI documentation against the implementation

## Changes

- **tool-permissions**: `skill` tool patterns match the absolute
`SKILL.md` path, not the skill name (fixed the table, example pattern,
and added a clarifying note).
- **external-agents**: Gemini CLI receives Zed's Google AI key when no
env key is set; extension-provided agents are deprecated in favor of the
ACP registry.
- **inline-assistant**: alternatives run alongside the inline assistant
model (not just the default model); fixed a broken anchor and
`gpt-4-mini` → `gpt-5-mini` model id typos.
- **mcp**: corrected the extensions menu item name ("Install New
Servers…"), the remote server `url` example, and removed the nonexistent
`thinking` tool from the profile example.
- **agent-panel**: "New From Summary" lives in the New Thread menu;
corrected the `@`-mention type list (no "instruction files"; added Fetch
and Branch Diff).
- **use-api-access**: DeepSeek default `api_url` includes `/v1`.
- **skills**: folder name is a convention not a requirement; long
descriptions warn rather than fail (measured in bytes); hidden skills
are also `@`-mentionable; dropped the unenforced consecutive-hyphen
rule; reconciled the no-remote-registry note with GitHub import.
- **edit-prediction**: `alt-tab` and `alt-l` are bound across platforms;
predictions are throttled rather than fired on every keystroke.
- **getting-started, windows-and-projects, parallel-agents**: Panel
Layout lives in the title-bar user menu, with
`workspace::UseAgenticLayout`/`UseClassicLayout` action references.

Release Notes:

- N/A

---------

Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>