fix(migrate): write a real clawhdf5-agent store

clawhdf5-migrate wrote a layout of its own (/chunks, /sessions,
/entities, /relations, root attributes, no /meta or schema_version) that
HDF5Memory::open rejects, so a "migrated" SQLite database could not be
used as agent memory — contrary to the README.

It now writes through the agent's own API (HDF5Memory::create/open,
save_batch, the session cache and the knowledge graph), so there is no
second copy of the schema:

- sessions and entities/relations carry over; deleted rows become
  deleted records (or are left out with --skip-deleted);
- embeddings follow the library default (float16), --f32 opts out and
  --float16 is a hidden no-op, as in clawhdf5-cli; the `half`-based
  conversion is gone;
- every source row is checked before the output is created: a wrong
  embedding length, an empty embedding, a dimension that differs from
  an existing store's, or a float16 value beyond +-65504 is an error
  naming the chunk id, and an existing store is left untouched;
- --incremental opens the existing store, adds only rows it does not
  hold (matched by content) and follows the source's deleted flags;
- a source with no memory rows needs --embedding-dim;
- validation reads the result back with HDF5Memory::open_read_only,
  compares every field (embeddings bit for bit, round_to_f16 of the
  source for float16) and checks a migrated record is found by search.

clawhdf5-agent gains HDF5Memory::sessions()/sessions_mut(),
HDF5Memory::delete_batch (one save, all-or-nothing, no auto-compact),
SessionCache::add_at, and re-exports SessionCache/SessionEntry.

The old layout's per-dataset SHA-256 provenance attributes have no place
in the agent schema and are gone. An adversarial review found two
blockers (silent truncation of long embeddings; an --incremental
dimension check that could never fire) and four majors (a failed run
wiping the existing store, dim-0 stores, deleted-flag drift); all are
fixed with regression tests. 42 migrate tests, incl. h5py opening a
migrated store.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-migrate/Cargo.toml

@@ -3,7 +3,7 @@ name = "clawhdf5-migrate"
 version = "2.7.0"
 edition = "2024"
 rust-version.workspace = true
-description = "CLI to migrate SQLite agent memory databases to HDF5 format"
+description = "CLI to migrate SQLite agent memory databases to clawhdf5-agent stores"
 license = "MIT"
 repository = "https://git.redclaw.dev/quantumclaw/clawhdf5"
 readme = "README.md"
@@ -17,10 +17,8 @@ path = "src/main.rs"
 [dependencies]
 clawhdf5-agent = { path = "../clawhdf5-agent", version = "2.7.0" }
 clawhdf5-format = { path = "../clawhdf5-format", version = "2.7.0" }
-clawhdf5 = { path = "../clawhdf5", version = "2.7.0" }
 rusqlite = { version = "0.31", features = ["bundled"] }
 clap = { version = "4", features = ["derive"] }
-half = { workspace = true }
 
 [dev-dependencies]
 tempfile = { workspace = true }