feat: add custom column support (#3089)

Configure the interactive search UI appearance. Resolves #998

```toml
[ui]
columns = ["duration", "time", "command"]
```

### `columns`

Default: `["duration", "time", "command"]`

Columns to display in the interactive search, from left to right. The
selection
indicator (`" > "`) is always shown first implicitly.

Each column can be specified as:
- A simple string (uses default width): `"duration"`
- An object with type and optional width/expand: `{ type = "directory",
width = 30 }`

#### Available column types

| Column | Default Width | Description |
| --------- | ------------- |
----------------------------------------------- |
| duration | 5 | Command execution duration (e.g., "123ms") |
| time | 8 | Relative time since execution (e.g., "59m ago") |
| datetime | 16 | Absolute timestamp (e.g., "2025-01-22 14:35") |
| directory | 20 | Working directory (truncated if too long) |
| host | 15 | Hostname |
| user | 10 | Username |
| exit | 3 | Exit code (colored by success/failure) |
| command | * | The command itself (expands by default) |

#### Column options

- **type**: The column type (required when using object format)
- **width**: Custom width in characters (optional, uses default if not
specified)
- **expand**: If `true`, the column fills remaining space. Default is
`true` for `command`, `false` for others. Only one column should have
`expand = true`.

#### Examples

```toml
# Minimal - more space for commands
columns = ["duration", "command"]

# With custom directory width
columns = ["duration", { type = "directory", width = 30 }, "command"]

# Show host for multi-machine sync users
columns = ["duration", "time", "host", "command"]

# Show exit codes prominently
columns = ["exit", "duration", "command"]

# Make directory expand instead of command
columns = ["duration", "time", { type = "directory", expand = true }, { type = "command", expand = false }]
```

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