terminal: Allow configuring conda manager (#40577)

Closes #40576
This PR makes Conda activation configurable and transparent by adding a
`terminal.detect_venv.on.conda_manager` setting (`"auto" | "conda" |
"mamba" | "micromamba"`, default `"auto"`), updating Python environment
activation to honor this preference (or the detected manager executable)
and fall back to `conda` when necessary.

The preference is passed via `ZED_CONDA_MANAGER` from the terminal
settings, and the activation command is built accordingly (with proper
quoting for paths). Changes span
`zed/crates/terminal/src/terminal_settings.rs` (new `CondaManager` and
setting), `zed/crates/project/src/terminals.rs` (inject env var),
`zed/crates/languages/src/python.rs` (activation logic), and
`zed/assets/settings/default.json` (document the setting). Default
behavior remains unchanged for most users while enabling explicit
selection of `mamba` or `micromamba`.

Release Notes:
- Added: terminal.detect_venv.on.conda_manager setting to choose the
Conda manager (auto, conda, mamba, micromamba). Default: auto.
- Changed: Python Conda environment activation now respects the
configured manager, otherwise uses the detected environment manager
executable, and falls back to conda.
- Reliability: Activation commands quote manager paths to handle spaces
across platforms.
- Compatibility: No breaking changes; non-Conda environments are
unaffected; remote terminals are supported.

---------

Co-authored-by: Lukas Wirth <me@lukaswirth.dev>
Co-authored-by: Lukas Wirth <lukas@zed.dev>

crates/language/src/toolchain.rs

@@ -9,7 +9,7 @@ use std::{path::PathBuf, sync::Arc};
 use async_trait::async_trait;
 use collections::HashMap;
 use fs::Fs;
-use gpui::{AsyncApp, SharedString};
+use gpui::{App, AsyncApp, SharedString};
 use settings::WorktreeId;
 use task::ShellKind;
 use util::rel_path::RelPath;
@@ -110,7 +110,7 @@ pub trait ToolchainLister: Send + Sync + 'static {
         fs: &dyn Fs,
     ) -> anyhow::Result<Toolchain>;
 
-    fn activation_script(&self, toolchain: &Toolchain, shell: ShellKind) -> Vec<String>;
+    fn activation_script(&self, toolchain: &Toolchain, shell: ShellKind, cx: &App) -> Vec<String>;
 
     /// Returns various "static" bits of information about this toolchain lister. This function should be pure.
     fn meta(&self) -> ToolchainMetadata;