chore(release): kyberforge 1.5.0, marketplace 0.4.0

Why
---
The SessionStart freshness hook is a new kyberforge feature and was committed
without a version bump. It also cannot ship unbumped: apm's executable-trust
allow key is version-pinned, so `kyberforge#1.4.1` would have stopped matching
the moment the package version moved, silently blocking the very hook the entry
exists to authorise.

Implementation notes
-----------------
kyberforge 1.4.1 -> 1.5.0 (MINOR, new feature); marketplace and root manifest
0.3.4 -> 0.4.0, following the convention in bb9158d where a package bump carries
the marketplace version with it. The executables.allow key moves to
kyberforge#1.5.0 in the same commit. Compiled manifests regenerated with
`apm pack` plus both sync scripts.

A bare `apm pack` also writes build/ and a root .claude-plugin/plugin.json,
neither of which is repo content — the pre-push gate only ever runs pack with
--dry-run, so they had not appeared before. Both removed; build/ is now
gitignored so a future release does not stage it by accident.

Impact
------
Consumers pinning kyberforge see a MINOR bump. All 15 pre-push hooks pass,
including apm pack --check-clean, so compiled output matches the manifests.

ADR: 0019

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X7GvKuJfy2WrdBmUttV4DT

.gitignore

@@ -40,3 +40,7 @@ apm_modules/
 # plugins/<name>/.apm/hooks/ (ADR-0019).
 .claude/hooks/
 .claude/apm-hooks.json
+
+# `apm pack` bundle output. The pre-push gate runs pack with --dry-run, so this
+# only appears after a bare `apm pack` during a release; it is not repo content.
+build/