Sync fork up to the latest zed-industries/zed upstream (6bca213, zed-industries#58037),
on top of the existing partial sync already on main (which reached zed-industries#57456).

Resolved conflicts:
- .gitignore: kept both the fork (/claude-code-ext/) and upstream
  (.nixos-test-history) entries.
- crates/proto/proto/zed.proto: integrated upstream Envelope fields 453-456
  (document links) alongside the fork's reserved claude-code-ide range
  (10000-10004).

Cargo.lock reconciled with cargo so it matches upstream's pins plus the
fork's claude_code_ide / claude_code_ide_server dependencies; verified with
`cargo metadata --locked`.

## Summary

While profiling agent sessions that make a lot of `edit_file`
operations, I noticed the LSP `textDocument/didChange` handler firing
excessively. Looking into this, I found out that the streaming edit
pipeline was applying each `CharOperation` from `StreamingDiff` as its
own `buffer.edit` transaction, and every transaction emits a
`BufferEvent::Edited` event. Each event can trigger several other
expensive events depending on whether the buffer is being rendered in an
editor or is registered with a language.

For example, there are `didChange` LSP events, the editor's on edit work
(matching brackets, bracket colorization, code actions, outline), and
more. A single `edit_file` could trigger hundreds of these at the higher
end in a single synchronous app update, which would block the foreground
thread for a bit and cause Zed to drop frames.

I fixed this by collecting all of a chunk's `CharOperation`s and
applying them in one `buffer.edit` call, so only a single
`BufferEvent::Edited` event gets emitted. This is safe because
operations are non overlapping by design of streaming diff (the edit
cursor only advances).

## Why this wasn't caught earlier

The cost only fully appears when a buffer is both registered with a
language server and rendered in an editor. Without that, most of the per
transaction observers never run, so the existing `edit_file_tool`
benchmark (which ran the tool against a bare buffer) didn't surface it.
I reworked the benchmark to open the edited buffer in an editor view,
register a fake language server with per edit diagnostics, and lay out a
frame, so it exercises the same cascade as the real editor. I also added
a larger fixture.

## Results

Measured with the `release-fast` profile on the reworked benchmark:

| Fixture | Initial file | Before | After | Improvement |
| --- | --- | --- | --- | --- |
| `tiny_function_rewrite` | 1.4 KB | 31.1 ms | 12.1 ms | −61% |
| `small_function_rewrite` | 3.0 KB | 42.4 ms | 19.3 ms | −55% |
| `medium_many_small_changes` | 4.6 KB | 309.2 ms | 151.5 ms | −51% |
| `medium_insertions` | 4.6 KB | 171.8 ms | 126.1 ms | −27% |
| `large_multi_edit` | 44 KB | 9,549 ms | 919 ms | −90% |

Self-Review Checklist:
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the UI/UX checklist
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:
- Improved agent's edit file tool performance

Sync fork up to the latest zed-industries/zed upstream (8ce658f, zed-industries#58579),
on top of the previous sync that reached 6bca213 (zed-industries#58037).

Resolved conflicts:
- crates/zed/src/main.rs: dropped the standalone `git_graph::init(cx)` call
  because upstream folded the `git_graph` crate into `git_ui` (the
  `git_ui::init` on the preceding line now invokes `git_graph::init`
  internally). Kept the fork-only `claude_code_ide::init(cx)` call.

Other fork-specific touch points (workspace `Cargo.toml`, `.gitignore`
`/claude-code-ext/` entry, `crates/proto/proto/zed.proto` reserved range
10000-10004, `crates/proto/src/proto.rs`, `crates/project/src/project.rs`,
`crates/project/src/terminals.rs`, `crates/remote_server/src/headless_project.rs`,
`crates/zed/Cargo.toml`, etc.) auto-merged cleanly against upstream's
changes; verified the fork additions (claude_code_ide crates,
claude_code_ide_dispatcher modules, script/build-fork.ps1, README header,
gpui_tokio shim) are intact.

Cargo.lock auto-merged; verified with `cargo metadata --locked`.