fix: report connection errors instead of "No results found!"

[DavidsonRafaelK]

Closes #1879.

Problem

When anidb_curl fails at the network level the body is empty, so the Just a moment check in anidb_search never fires and the empty result falls through to die "No results found!". A site outage, a dropped connection, a DNS failure and a genuinely unknown anime all produced the same message. That is what the current anidb.app outage in #1877 looks like from the user side.

There is a second half to it. Both scrapers are called inside a command substitution:

anime_list=$(anidb_search "$query")

so die only exits the subshell. The message is printed, the parent keeps going with an empty variable, and reaches the next die. A cloudflare block today prints both lines:

$ sh demo.sh          # die inside $( ), reduced to the essentials
Blocked by cloudflare. Try installing curl-impersonate
No results found!

Change

• Empty-response guard in anidb_search and anidb_episodes, the two scrapers where an empty body is never a legitimate answer. It names the host: Connection error: no response from https://anidb.app.
• || exit 1 at the four call sites, so the message the subshell printed actually stops the run instead of being followed by a second, contradictory one.
• Version bumped to 5.0.4.

anidb_desc is deliberately untouched: its metadata is optional and the caller already writes anidb_desc "$anime_id" || true. process_hist_entry is untouched too, since it runs backgrounded per history entry.

Before / after

Same binary, base_api pointed at a blackhole address (198.51.100.1) to force the timeout path:

=== 5.0.3 ===
Checking dependencies...
No results found!

=== patched ===
Checking dependencies...
Connection error: no response from https://198.51.100.1

Checks

• shellcheck -s sh -o all -e 2250 ani-cli — clean
• shfmt -i 4 -ci -d ani-cli — clean
• test -x ani-cli — ok
• no awk, no wget added
• version_number bumped, so the version-bump job sees it
• README needs no change: no flags, no behaviour outside the error path

Commit is co-authored by the agent that helped write it, as requested in #1879.