[Andrew-Velox]

Fixes #5

Adds the fastfetch-style overrides asked for in #5: rename a built-in row, replace its reading with a string, or take its value from a command.

Config

modules = ["os", "kernel", "uptime", "custom", "shell"]

[overrides.os]
label = "Distro"                 # rename only

[overrides.kernel]
value = "my-own-kernel 1.0"      # fixed text instead of the reading

[overrides.uptime]
label = "Up"
command = "uptime -p"            # first line of the output

[[custom]]
label = "Public IP"
command = "curl -s --max-time 1 ifconfig.me"   # custom rows take a command too

New key: command_timeout (default 1s, clamped to 0.1-10).

Behaviour

• label is display-only. The row keeps its icon, its place and its --live updates. iconic and tree print no names, so a rename does not show there.
• value / command replace the row's figures and bars with plain text, and the row is excluded from --live refresh so it is not overwritten.
• A module the machine cannot read (e.g. battery on a desktop) still shows the user's text if they override it.
• Commands run once at startup through sh -c with the user's privileges, all started together, so the wait is the slowest one rather than the sum. Only the first non-empty line is used, with control characters stripped. Nothing printed, or longer than command_timeout, leaves the row out.
• Mistakes (unknown module, value with command, empty table, empty label, overriding colors/custom) are reported at load, and config errors now include the line number.
• Existing configs are unchanged: custom = [{ label, value }] parses as before.

Implementation

• src/rows.rs: Source, CustomRow, Override, validated at parse time.
• src/fetch/command.rs: the one process runner (deadline, process group kill, output cap), now shared with the version probes in detail.rs.
• Item gains a private display name next to its identity label; styles use it where they print a label.
• fetch::gather plans the rows first so every command can start before any is waited on.

Testing

• 435 tests pass (428 with --no-default-features), including a width sweep of long custom names across every style and tests that a refresh never overwrites an override.
• clippy -D warnings and cargo doc -D warnings clean on 1.98.1 and a recent nightly; macOS targets compile.
• Run by hand with a real config in the classic, boxed, card and minimal styles, including a command that exceeds the timeout.