fix(ssh): POST /computers/:alias/test hangs after successful SSH connect

The test endpoint's runProbe() waited for the ssh2 stream's 'close' event,
which some SSH servers never emit for short-lived exec channels (the command
'true' exits instantly). This caused the promise to hang forever — the HTTP
response never returned, and the FE's Test spinner spun indefinitely.

Three fixes:

1. runProbe now resolves on the 'exit' event (not 'close') — the command has
   finished and the exit code is available. 'close' is kept as a fallback.
   Stream data/stderr are drained to prevent buffer deadlocks.

2. runProbe has a 15s timeout safety net — if the exec callback or 'exit'
   event never fires (e.g. server requires a pty for exec), the probe
   resolves false instead of hanging forever.

3. The entire test() method is wrapped in a 30s Promise.race timeout —
   even if pool.acquire() or pool.drop() hangs, the endpoint ALWAYS
   responds with { ok, error? }.

The probe is fully non-interactive (no blocking prompts). tsc EXIT 0,
biome clean, 1756 tests pass.

0 files changed, 0 insertions, 0 deletions