init: install hooks + scaffold config; load-context: inline instructions

poc-memory init now:
- Creates the data directory
- Installs the memory-search hook into Claude settings.json
- Scaffolds a starter config.jsonl if none exists

load-context now prints a command reference block at the top so the
AI assistant learns how to use the memory system from the memory
system itself — no CLAUDE.md dependency needed.

Also extract install_hook() as a public function so both init and
daemon install can use it.

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

config.example.jsonl

@@ -0,0 +1,19 @@
+// poc-memory configuration
+// Copy to ~/.config/poc-memory/config.jsonl and edit.
+
+{"config": {
+  "user_name":      "Alice",
+  "assistant_name": "Assistant",
+  "data_dir":       "~/.claude/memory",
+  "projects_dir":   "~/.claude/projects",
+  "core_nodes":     ["identity.md"],
+  "journal_days":   7,
+  "journal_max":    20
+}}
+
+// Context groups loaded at session start, in order.
+// source types: "store" (default), "file" (from data_dir), "journal"
+
+{"group": "identity",    "keys": ["identity.md"]}
+{"group": "journal",     "source": "journal"}
+{"group": "orientation", "keys": ["where-am-i.md"], "source": "file"}