feat(youtube): route yt-dlp through SSH host for residential IP egress

Adds LAST30DAYS_YT_SSH_HOST env var (or `~/.config/last30days/.env` key).
When set, yt-dlp YouTube search invocations are wrapped as
`ssh <host> "yt-dlp ..."` so they run on a residential-IP machine.

Motivation: when last30days runs on a datacenter VPS (Hetzner,
DigitalOcean, AWS, etc.), `ytsearch:` queries return 0 results because
YouTube's bot-wall fingerprints datacenter IP ranges before any cookie
check runs. Cookies alone don't fix this — the IP reputation is checked
first. Verified across yt-dlp stable 2026.03.17 and nightly builds.

The existing fallbacks (browser cookies, residential proxy services,
excluding YouTube) all have downsides: cookies expire, proxies cost
money, exclusion loses signal. Many users with a Mac mini, Pi, or
home server can host yt-dlp on their own residential IP — this just
needs an SSH alias and a one-line env var to wire it up.

Behaviour:
- Default (env var unset): identical to before, no shape change.
- Env var set: search command list is wrapped with `ssh -o BatchMode=yes
  <host> "<shell-quoted yt-dlp invocation>"`. is_ytdlp_installed()
  returns True without a local PATH check (the binary lives on the
  remote host).
- Transcript path: when SSH-routing is on, skips the yt-dlp transcript
  path (which writes a VTT file we couldn't easily read back over SSH)
  and uses the existing _fetch_transcript_direct HTTP fallback. The
  timedtext API isn't bot-walled, so this works fine on datacenter IPs.

Setup pitfall documented in the function docstring: on macOS hosts
with Homebrew, `eval "$(/opt/homebrew/bin/brew shellenv zsh)"` must
live in ~/.zshenv (not just ~/.zprofile) — non-login SSH shells don't
source .zprofile, so without this `ssh macmini "yt-dlp ..."` returns
"command not found" while interactive SSH works fine.

Tests: 10 new cases covering env var read, whitespace stripping,
empty-value handling, command wrapping passthrough/active modes,
shlex quoting, is_ytdlp_installed short-circuit, and end-to-end
search_youtube wrapping. Full test suite: 0 new failures (the 14
pre-existing failures in test_store, test_watchlist, test_setup_openclaw,
test_safari_cookies, test_version_consistency are unchanged on main).

Verified live: 0 results → 4 real hits for "claude code" search from a
Hetzner VPS routed through a Mac mini exit node on Tailscale.

skills/last30days/scripts/last30days.py

@@ -541,6 +541,13 @@ def main() -> int:
 
     config = env.get_config()
 
+    # Surface SSH-routing config as an env var so library modules (e.g.
+    # youtube_yt) can read it without taking a config dependency. This
+    # routes yt-dlp through `ssh <host>` to bypass YouTube's bot-wall on
+    # datacenter IPs (see lib/youtube_yt.py for details).
+    if config.get("LAST30DAYS_YT_SSH_HOST") and "LAST30DAYS_YT_SSH_HOST" not in os.environ:
+        os.environ["LAST30DAYS_YT_SSH_HOST"] = config["LAST30DAYS_YT_SSH_HOST"]
+
     # Handle setup subcommand
     topic = " ".join(args.topic).strip()
     if topic.lower() == "setup":