fix(kyberforge): target-neutral hook token and accurate hook reach docs

Switch the SessionStart hook to apm's target-neutral ${PLUGIN_ROOT} token.
Two scratch packages differing only in the token deploy byte-identical
SessionStart entries with apm 0.28.0, matching the committed
.claude/settings.json, so the deployed output does not change. The test
pin in tests/test-apm-current-hook.sh moves with it.

Correct the claim that Copilot loads no hooks from kyberforge. targets:
is package-wide, so apm also writes .github/hooks/kyberforge-hooks.json
(nested shape passed through, runtime unverified) and merges into
.codex/hooks.json when .codex/ exists. Recorded as accepted in an
ADR-0019 amendment dated 2026-09-28; README and docs/hooks.md updated.

Refs #94

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KkT7RSDwDbmrM9T34b6sTi

plugins/kyberforge/.apm/hooks/hooks.json

@@ -4,7 +4,7 @@
       {
         "hooks": [
           {
-            "command": "${CLAUDE_PLUGIN_ROOT}/.apm/hooks/check-apm-current.sh",
+            "command": "${PLUGIN_ROOT}/.apm/hooks/check-apm-current.sh",
             "timeout": 380,
             "type": "command"
           }