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/profiler/test_session_profile.py

@@ -1,55 +0,0 @@
-"""
-Tests for the session_profile table + repo helpers (SIGNAL_CAPTURE_AUDIT gap #2).
-
-Pre-v1 the ingestion job that populates keystroke-dynamics features is
-deferred; this suite exercises the empty-write path (one row per session,
-all feature columns NULL) and round-trips a filled row so future work can
-land without re-discovering the schema.
-"""
-import pytest
-from decnet.web.db.factory import get_repository
-
-
-@pytest.fixture
-async def repo(tmp_path):
-    r = get_repository(db_path=str(tmp_path / "session_profile.db"))
-    await r.initialize()
-    return r
-
-
-@pytest.mark.anyio
-async def test_empty_write_path_ships_null_features(repo):
-    # Session close writes `{}` — schema_version defaults to 1, all feature
-    # columns stay NULL.
-    await repo.upsert_session_profile("sid-1", {})
-    row = await repo.get_session_profile("sid-1")
-    assert row is not None
-    assert row["sid"] == "sid-1"
-    assert row["schema_version"] == 1
-    assert row["kd_iki_mean"] is None
-    assert row["kd_digraph_simhash"] is None
-    assert row["total_keystrokes"] is None
-
-
-@pytest.mark.anyio
-async def test_upsert_replaces_existing(repo):
-    await repo.upsert_session_profile("sid-2", {})
-    await repo.upsert_session_profile(
-        "sid-2",
-        {
-            "kd_iki_mean": 0.120,
-            "kd_iki_p95": 0.450,
-            "total_keystrokes": 512,
-            "session_duration_s": 61.3,
-        },
-    )
-    row = await repo.get_session_profile("sid-2")
-    assert row["kd_iki_mean"] == pytest.approx(0.120)
-    assert row["kd_iki_p95"] == pytest.approx(0.450)
-    assert row["total_keystrokes"] == 512
-    assert row["session_duration_s"] == pytest.approx(61.3)
-
-
-@pytest.mark.anyio
-async def test_get_missing_returns_none(repo):
-    assert await repo.get_session_profile("does-not-exist") is None