fix: enable prompts when installing via curl|bash

[glauberlima]

Summary

• is_piped() checked stdin (-t 0) to decide whether to show interactive prompts
• When running via curl ... | bash, stdin is the pipe carrying the script — so prompts were silently skipped and defaults applied
• Fix: check stdout (-t 1) instead, which remains a tty in the curl|bash scenario

Root Cause

# Before — stdin-based (wrong for curl|bash)
is_piped() { [[ ! -t 0 ]]; }

# After — stdout-based (correct signal: is a human watching?)
is_piped() { [[ ! -t 1 ]]; }

The read calls already use /dev/tty so they can handle piped stdin — the guard was the only thing blocking the prompts.

Behaviour Matrix

Scenario	stdout fd 1	Result
curl ... | bash	IS a tty	shows prompts ✓
./install.sh	IS a tty	shows prompts ✓
CI / ./install.sh > log	NOT a tty	uses defaults silently ✓
./install.sh | tee log	NOT a tty	uses defaults silently ✓

Test plan

• bash <(cat install.sh) — language and component menus appear
• ./install.sh > /tmp/log.txt 2>&1 — prompts skipped, defaults used
• ./install.sh — interactive flow unchanged
• ./tests/shellcheck.sh passes (verified ✓)