[0.1.7] Fix error display when docscribe fails and trailing literal suppresses warnings

[unurgunite]

Description

Fixes the annotator swallowing docscribe failures and the trailing-literal cache bug. When docscribe exits with an error (missing gem, syntax error, or error_count>0 with no files) the previous code cached an empty result and rendered it as 0 — the real error was only visible in the daemon. Now failures are surfaced and not cached.

Changes

• DocscribeAnnotator.doAnnotate no longer treats !success as null with 0 offenses. Failed runs log success/exit/stderr to idea.log, show a visible annotation, and are not cached. A blank stdout with success is still cached as a clean file.
• error_count>0 && files.isEmpty() (e.g. parser error or trailing []/:sym/42 suppressing InvalidType) now creates a synthetic Docscribe/Error offense on line 1 instead of being collapsed to null and hidden.
• The synthetic error path is excluded from DocscribeAnnotatorCache to avoid poisoning the cache and to allow the next annotation to retry the daemon.
• gem not installed (exit 2, stderr contains docscribe gem is not installed) is now shown as a BALLOON WARNING with an Add to Gemfile action that appends gem "docscribe" to the project Gemfile root (so CI picks it up) and opens the file, mirroring RuboCop's UX. fatal and parser errors remain as red ERROR squiggles.

Checklist

• Tests pass (./gradlew test — 238 tests)
• Formatting clean (./gradlew spotlessCheck)
• Static analysis clean (./gradlew detekt)
• Plugin verified (./gradlew verifyPlugin against 261.* / 262.*)
• CHANGELOG updated (if applicable)