…ll level (zed-industries#44835)

Fixes zed-industries#33958

## Problem

When opening a terminal in Zed, `SHLVL` incorrectly starts at 2 instead
of 1. On `workspace: reload`, it increases by 2 instead of 1.

## Root Cause

1. Zed's `shell_env::capture()` spawns a login shell (`-l -i -c`) to
capture the user's environment, which increments `SHLVL`
2. The captured `SHLVL` is passed through to the PTY options
3. When alacritty_terminal spawns the user's shell, it increments
`SHLVL` again

Result: `SHLVL` = captured value + 1 = 2 (when launched from Finder)

## Solution

Remove `SHLVL` from the environment in `TerminalBuilder::new()` before
passing it to alacritty_terminal. This allows the spawned shell to
initialize `SHLVL` to 1 on its own, matching the behavior of standalone
terminal emulators like iTerm2, Kitty, and Alacritty.

## Testing

- Launch Zed from Finder → open terminal → `echo $SHLVL` → should output
`1`
- Launch Zed from shell → open terminal → `echo $SHLVL` → should output
`1`
- `workspace: reload` → open terminal → `echo $SHLVL` → should remain
`1`
- Tested with bash, zsh, fish

Release Notes:

- Fixed terminal `$SHLVL` starting at 2 instead of 1
([zed-industries#33958](zed-industries#33958))

Fixes #33958

## Problem

PR #44835 attempted to fix SHLVL starting at 2 by removing it from the
`env` HashMap passed to alacritty. However, that HashMap is only an
**overlay** — alacritty uses the parent process environment as a base
and applies the overlay on top. Since alacritty never calls
`env_remove("SHLVL")`, the terminal shell still inherits `SHLVL` from
Zed's process environment.

## Root Cause

The real issue is in `load_login_shell_environment()`:

1. `shell_env::capture()` spawns a login shell to capture environment
variables
2. That login shell increments `SHLVL` (from 0→1 or n→n+1)
3. The captured env (including the incremented `SHLVL`) is written to
Zed's **process environment** via `env::set_var`
4. When you open a terminal, the shell inherits Zed's `SHLVL` and
increments it again → starts at 2
5. On reload, `shell_env::capture()` runs again with the
already-elevated `SHLVL`, incrementing it further → +2 per reload

## Fix

Skip `SHLVL` when setting Zed's process environment in
`load_login_shell_environment()`. This prevents the login-shell capture
from polluting Zed's env, so terminals start fresh with the correct
`SHLVL`.

Fixes #33958

## Problem

PR #44835 attempted to fix SHLVL starting at 2 by removing it from the
`env` HashMap passed to alacritty. However, that HashMap is only an
**overlay** — alacritty uses the parent process environment as a base
and applies the overlay on top. Since alacritty never calls
`env_remove("SHLVL")`, the terminal shell still inherits `SHLVL` from
Zed's process environment.

## Root Cause

The real issue is in `load_login_shell_environment()`:

1. `shell_env::capture()` spawns a login shell to capture environment
variables
2. That login shell increments `SHLVL` (from 0→1 or n→n+1)
3. The captured env (including the incremented `SHLVL`) is written to
Zed's **process environment** via `env::set_var`
4. When you open a terminal, the shell inherits Zed's `SHLVL` and
increments it again → starts at 2
5. On reload, `shell_env::capture()` runs again with the
already-elevated `SHLVL`, incrementing it further → +2 per reload

## Fix

Skip `SHLVL` when setting Zed's process environment in
`load_login_shell_environment()`. This prevents the login-shell capture
from polluting Zed's env, so terminals start fresh with the correct
`SHLVL`.

…ries#46273)

Fixes zed-industries#33958

## Problem

PR zed-industries#44835 attempted to fix SHLVL starting at 2 by removing it from the
`env` HashMap passed to alacritty. However, that HashMap is only an
**overlay** — alacritty uses the parent process environment as a base
and applies the overlay on top. Since alacritty never calls
`env_remove("SHLVL")`, the terminal shell still inherits `SHLVL` from
Zed's process environment.

## Root Cause

The real issue is in `load_login_shell_environment()`:

1. `shell_env::capture()` spawns a login shell to capture environment
variables
2. That login shell increments `SHLVL` (from 0→1 or n→n+1)
3. The captured env (including the incremented `SHLVL`) is written to
Zed's **process environment** via `env::set_var`
4. When you open a terminal, the shell inherits Zed's `SHLVL` and
increments it again → starts at 2
5. On reload, `shell_env::capture()` runs again with the
already-elevated `SHLVL`, incrementing it further → +2 per reload

## Fix

Skip `SHLVL` when setting Zed's process environment in
`load_login_shell_environment()`. This prevents the login-shell capture
from polluting Zed's env, so terminals start fresh with the correct
`SHLVL`.

…ries#46273)

Fixes zed-industries#33958

## Problem

PR zed-industries#44835 attempted to fix SHLVL starting at 2 by removing it from the
`env` HashMap passed to alacritty. However, that HashMap is only an
**overlay** — alacritty uses the parent process environment as a base
and applies the overlay on top. Since alacritty never calls
`env_remove("SHLVL")`, the terminal shell still inherits `SHLVL` from
Zed's process environment.

## Root Cause

The real issue is in `load_login_shell_environment()`:

1. `shell_env::capture()` spawns a login shell to capture environment
variables
2. That login shell increments `SHLVL` (from 0→1 or n→n+1)
3. The captured env (including the incremented `SHLVL`) is written to
Zed's **process environment** via `env::set_var`
4. When you open a terminal, the shell inherits Zed's `SHLVL` and
increments it again → starts at 2
5. On reload, `shell_env::capture()` runs again with the
already-elevated `SHLVL`, incrementing it further → +2 per reload

## Fix

Skip `SHLVL` when setting Zed's process environment in
`load_login_shell_environment()`. This prevents the login-shell capture
from polluting Zed's env, so terminals start fresh with the correct
`SHLVL`.