fix(money): count per-agent advisor artifacts in sessions scan

[rz1989s]

Problem

The money line under-counted advisor spend. scanMoney walked <repo>/<session-dir>/*.jsonl (main sessions, subagent <Agent>.jsonl, main __advisor.jsonl) but never entered the per-agent subtrees — <repo>/<session-dir>/<Agent>/__advisor.jsonl sits one level deeper and was silently skipped.

Advisor artifacts carry the standard usage.cost.total shape, so this was real spend missing from DAY/7DAY/30DAY.

Measured impact (live sessions tree, 2026-10-12)

Window	Before	Missed	Undercount
DAY	$6.87 (168.1M tok)	+$1.91 (48.8M)	27.9%
7DAY	$137.56 (3.64B)	+$30.33 (861.9M)	22.0%
30DAY	$1336.74 (12.2B)	+$30.33	2.3%

157 files / ~6.8k entries affected. Depth 5 verified empty — no recursion needed, one extra level covers the tree completely.

Change

• scanSessionDir(): walks the session dir itself plus per-agent subtrees one level deeper.
• Test fixture pins nested-advisor coverage (windows, sub share, entry count).
• README money bullet + /sl notify docs name both __advisor.jsonl levels; sub field comment now reads "subagent + advisor artifact share".

Verify

• typecheck + 62/62 tests pass
• Rescan of real tree after fix: DAY $8.93 (221.2M) · 7DAY $168.03 (4.5B) · 30DAY $1367.21 (13.1B) — deltas reconcile exactly with the measured gap
• Global message-id dedupe unchanged (resumed/branched copies still count once)