feat(rulings): a command or edit touching an area's files shows its rulings, once per session (milestone 444 step 4, #4757)

A System's rulings (the Rulings section of its description) now reach the
work by path, not by similarity. Both PreToolUse arms resolve the files a
command or edit names to the Systems whose path_patterns cover them, and the
first touch in a session shows each area's rulings in one line; a repeat is
a one-line reference. A lookup, so no floor, no budget, no retrieval_logs row.

- services/system_rulings: parse_rulings, command_paths (reads and writes,
  relative to the repo root from any cwd; flags, URLs, globs skipped),
  rulings_for_paths
- /tool-rules takes root, cwd and seen_ruling_systems; /prior-art takes
  seen_ruling_systems; both return ruling_system_ids
- hooks share <sid>.rulings.ids (cleared on compaction by the ledger naming
  convention); the Bash hook sends the repo root and cwd
- system_usage_events (migration 0114): surfacings by source, pulls from
  get_system; carried by backup (v20) through the system map
- writing-records: rulings also arrive when the area's files are touched

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

alembic/versions/0114_system_usage_events.py

@@ -0,0 +1,45 @@
+"""system_usage_events — were an area's rulings read once its files were
+touched? (milestone 444 step 4, #4757)
+
+Revision ID: 0114
+Revises: 0113
+Create Date: 2026-10-03
+
+The usage twin for Systems, beside note_usage_events and rule_usage_events and
+separate from both for the same reason they are separate from each other: a
+System id restores through its own map. FK-free like its siblings; no CHECK on
+`event`, like its siblings.
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0114"
+down_revision = "0113"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "system_usage_events",
+        sa.Column("id", sa.BigInteger(), primary_key=True),
+        sa.Column(
+            "created_at", sa.DateTime(timezone=True), nullable=False,
+            server_default=sa.text("now()"),
+        ),
+        sa.Column("user_id", sa.BigInteger(), nullable=True),
+        sa.Column("system_id", sa.BigInteger(), nullable=False),
+        sa.Column("event", sa.Text(), nullable=False),
+        sa.Column("source", sa.Text(), nullable=False),
+        sa.Column("project_id", sa.BigInteger(), nullable=True),
+    )
+    op.create_index(
+        "ix_system_usage_system_event", "system_usage_events", ["system_id", "event"]
+    )
+    op.create_index("ix_system_usage_created_at", "system_usage_events", ["created_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_system_usage_created_at", table_name="system_usage_events")
+    op.drop_index("ix_system_usage_system_event", table_name="system_usage_events")
+    op.drop_table("system_usage_events")