feat(web): drop SessionProfile, wire observations into AttackerDetail (DEBT-050 / DEBT-036 closure)

Destructive half of BEHAVE-INTEGRATION.md Phase 1. SessionProfile +
its kd_* columns + the dialect ALTER TABLE migration helpers are
deleted outright; pre-v1, the table shipped empty, no migration
ceremony required (per the no-new-_migrate_-pre-v1 memory rule).
DEBT-036 closes via DEBT-050 supersedure. AttackerDetail's
``observations`` field is wired to the new ``observations`` table
and returns an empty list until the BEHAVE-SHELL extractor (DEBT-050
Phase 2) starts emitting.

decnet/web/db/models/attackers.py — SessionProfile class deleted
(~135 lines), KD_PAUSE_*/KD_START_OF_ACTION_IDLE_S module constants
deleted, module docstring updated to point at the observations
table. AttackerIdentity.kd_digraph_simhash is KEPT — it's the v2
federation centroid hook, not a SessionProfile field; docstring
repointed to the BEHAVE primitive that will populate it.

decnet/web/db/sqlmodel_repo/attackers/sessions.py — DELETED.
SessionProfilesMixin dropped from the AttackersMixin MRO.

decnet/web/db/repository.py — abstract upsert_session_profile +
get_session_profile removed.

decnet/web/db/sqlite/repository.py + mysql/repository.py —
_migrate_session_profile_table helpers and their initialize() calls
removed. mysql initialize() now goes attackers → column_types →
admin (no session_profile step).

decnet/web/db/models/__init__.py — SessionProfile re-export gone.

decnet/web/db/models/attacker_intel.py — docstring cross-reference
to SessionProfile.schema_version retargeted to AttackerIdentity.

decnet/web/router/attackers/api_get_attacker_detail.py — adds
``observations: []`` to the response by calling
``repo.latest_observation_per_primitive(uuid)`` and projecting to a
list sorted by primitive path. Empty until the extractor lands;
shape matches BEHAVE-INTEGRATION.md §"AttackerDetail consumer".

tests/profiler/test_session_profile.py — DELETED (56 lines).
tests/db/test_base_repo.py — DummyRepo loses upsert_session_profile
and get_session_profile overrides.
tests/db/mysql/test_mysql_migration.py — initialize-call-order
assertion updated; session_profile step removed from the expected
sequence; docstring records why.
tests/ttp/test_lifter_absence.py — docstring "no SessionProfile" →
"no ObservationRow".

tests/ttp/test_lifter_absence.py

@@ -2,7 +2,7 @@
 
 Every per-source lifter is allowed (and expected) to encounter
 events whose required join is missing — no ``AttackerIntel`` row,
-no ``SessionProfile``, no ``AttackerBehavior``, no canary record,
+no ``ObservationRow``, no ``AttackerBehavior``, no canary record,
 no identity row, no ``CredentialReuse`` entry. Absence is the
 steady state, not the exception. The contract pinned here: