fix: address external audit — criticals 1-5 + mediums

Critical 1 (approval forgery): audit_log is now hash-chained
(prev_hash/entry_hash, verify_audit_chain); executor approve REQUIRES a
BIP-340 signature over sha256(cayce-ops:approve:<id>) when
CAYCE_OPS_OPERATOR_PUBKEY is set; deploy/roles.sql ships least-privilege
per-daemon DB roles.

Critical 2 (threading dead): sends create real OUTBOUND rows (own
Message-ID, In-Reply-To -> inbound); inbound message_id never overwritten;
maild compose adds the first-contact path; _match_proposal falls back to
inbound chains.

Critical 3 (duplicate sends): per-message transactions in send path —
SMTP failure on message N no longer resurrects 1..N-1; failures audited
(send_failed) and the row stays queued.

Critical 4 (classifier): negated approvals (cannot accept / not approved /
not accepting) classify REJECTION at 0.95 before the bare-keyword rule;
LLM prompt braces escaped (.format no longer KeyError into silent fallback).

Critical 5 (systemd): every daemon has a run subcommand
(maild run = poll+send, publisher run = publish-due, monitor run = build);
deploy README documents the separate daily publisher plan timer.

Mediums: approved_hash binds drafts/captions to the approved text (edited
text refuses to send/publish until re-approved); risk_score renamed
match_score (migration 0002) and auto-approve orders HIGHEST relevance
first; compose binds postgres to 127.0.0.1; IMAP marks \\Seen only after
commit (fetch returns (num, raw), mark post-commit); disabled channels are
terminal (ContentStatus.SKIPPED) and publish failures burn a bounded
attempt budget before abandonment; make hooks installs the pre-push gate.

tests: 12 new — 56 total, all green; ruff 0 findings; gitleaks clean.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: check lint test migrate-check leaks sync
+.PHONY: check lint test migrate-check leaks sync hooks
 
 sync:            ## install locked deps (creates .venv)
 	uv sync --frozen
@@ -17,5 +17,9 @@ migrate-check:   ## smoke the alembic chain on a scratch sqlite db
 leaks:           ## gitleaks over the full history
 	gitleaks detect --source . --log-opts="--all" -v
 
+hooks:            ## install the pre-push gate as a git hook (part of setup)
+	git config core.hooksPath scripts/githooks
+	@echo "pre-push gate installed (scripts/githooks/pre-push)"
+
 check: lint test migrate-check leaks   ## the pre-push gate — must be green before every push
 	@echo "check: OK"