docs: Apply brand voice standards to AI documentation (#48401)

## Summary

Reviewed and updated all 18 files in `docs/src/ai/` to meet Zed's brand
voice standards. Each file was scored against the 8-criterion rubric and
rewritten where needed to achieve 4+ on all criteria.

**Changes include:**
- Remove "Learn how to/about" patterns (8 instances)
- Replace vague phrases ("various types of tasks", "and more") with
specific examples
- Remove taboo words ("seamless", "naturally extends")
- Remove emotional language ("We're excited/thrilled/happy")
- Remove marketing patterns ("Stay tuned!", exclamation points)
- Remove unverifiable claims ("world's fastest")
- Replace hedging with direct statements
- Remove promotional emphasis (`_free_`, `**_for free_**`)
- Fix typo in external-agents.md ("servers" → "serves")
- Fix broken link syntax for Ollama Turbo

## Test plan

- [x] `mdbook build` succeeds
- [x] Grep for remaining taboo phrases (only one "seamless" in MCP
official quote, preserved intentionally)
- [x] All facts preserved (URLs, keybindings, settings keys, prices,
model names)

Fixes AI-8

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

docs/src/linux.md

@@ -2,7 +2,7 @@
 
 ## Standard Installation
 
-For most people we recommend using the script on the [download](https://zed.dev/download) page to install Zed:
+The installation script on the [download](https://zed.dev/download) page is the fastest way to install Zed:
 
 ```sh
 curl -f https://zed.dev/install.sh | sh