fix(init): use isatty(0) for TTY detection and add diagnostic probe

[BYK]

Summary

• Align the init wizard's TTY guard with the rest of the codebase by using isatty(0) from node:tty instead of process.stdin.isTTY (unreliable in Bun on inherited fds)
• Defensively backfill process.stdin.isTTY when isatty(0) reports true but the property is undefined, preventing @clack/core from silently skipping setRawMode
• Add an opt-in diagnostic probe (SENTRY_INIT_DIAGNOSTICS=1) for future TTY-related bug reports

Context

A user reported that curl -fsSL https://cli.sentry.dev/install | SENTRY_INIT=1 bash installs the binary but the first @clack/prompts confirm prompt doesn't register keystrokes. The install script correctly runs exec "$sentry_bin" init </dev/tty to reattach stdin to the terminal.

Investigation result: We could not reproduce the bug with the current HEAD binary. Both the piped reproducer (bash -c 'exec ./sentry init </dev/tty' < /dev/null) and the plain interactive run showed healthy TTY signals and accepted keystrokes normally.

However, the init wizard was the last remaining site in the codebase still using process.stdin.isTTY for TTY detection. Six other sites (src/cli.ts, mutate-command.ts, commands/log/view.ts, commands/auth/login.ts, seer-trial.ts, commands/trial/start.ts) already use isatty(0) precisely because process.stdin.isTTY is known to be unreliable in Bun's single-file binary. This change closes that consistency gap.

Diagnostic probe

The new SENTRY_INIT_DIAGNOSTICS=1 env var dumps a snapshot of stdin/stdout TTY state to stderr at two points: wizard entry and before the first prompt. If the bug resurfaces, reporters can include this output for targeted diagnosis instead of us guessing. Zero overhead when disabled.

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Semver Impact of This PR

🟢 Patch (bug fixes)

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Bug Fixes 🐛

Init

• Use isatty(0) for TTY detection and add diagnostic probe by BYK in #767

• Reuse detected existing project data by betegon in #766
• Ensure project reuse and spinner states by MathurAditya724 in #763

Internal Changes 🔧

• Regenerate docs by github-actions[bot] in e02799c1

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Codecov Results 📊

✅ 134 passed | Total: 134 | Pass Rate: 100% | Execution Time: 0ms

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 1649 uncovered lines.
✅ Project coverage is 95.5%. Comparing base (base) to head (head).

Coverage diff

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+ Coverage    95.50%    95.50%        —%
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  Files          253       254        +1
  Lines        36666     36676       +10
  Branches         0         0         —
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+ Hits         35019     35027        +8
- Misses        1647      1649        +2
- Partials         0         0         —

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