feat(route): give the advisor a writer, on a need and per row

route.sh now emits `--advisor opus` into the startup command it prints.
The flag existed and worked, but nothing generated it, so it went unused:
the only mechanism that ever set an advisor here was `/advisor`, which
writes the global advisorModel setting -- every session, every repo -- and
was abandoned for burning quota. Nothing replaced it.

Two independent triggers, almost disjoint by construction:

  rows 1-2  always. Sonnet main model, so opus is a capability LIFT rather
            than a peer. Load-bearing: every fallback is one row cheaper and
            the cheap rows are Sonnet, so this makes the quota fallback safe.
  rows 3-4  only at reversibility=costly|one-way. Opus main model, so the
            advisor buys peer review where a mistake is not cheap to undo.
  rows 5-6  never. The CLI rejects every advisor for a Fable main model.

costly forces row 3 and one-way forces row 4, so a Sonnet row always has
reversibility=cheap and neither rule reaches the other's rows.
verification=none is deliberately not a third trigger: beyond the stakes
rule it adds only cheap-to-reverse mistakes, docs sessions among them.
Applied per ROW, so fallback-command carries its own correct answer.

route-selftest.sh 56 -> 73. Section 14 gates the three CLI facts the rule
rests on against the installed claude without spending a token: advisor
validation runs before the empty-prompt check, so `-p ""` reaches the
validator and stops. --help cannot gate this -- it short-circuits before
option validation, so an unknown flag would pass the gate untested.

Three pre-existing checks updated rather than worked around: two asserted
whole command strings that now carry the advisor, and section 11's effort
extraction swallowed the tail of the command line.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X8N8hQEJSWWtieWUx37txT

package.json

@@ -1,6 +1,6 @@
 {
   "name": "repo-mailbox",
-  "version": "0.12.1",
+  "version": "0.13.0",
   "private": true,
   "type": "module",
   "engines": {