docs: link upstream ASET ecosystem

[attractor-set]

Summary

Add explicit upstream ecosystem links for the ASET Network Python + SQLite reference implementation.

This change:

• links the normative ASET Seed specification;
• links the normative ASET Network Extension;
• links the base non-normative aset-python-sqlite implementation;
• links this repository explicitly through project metadata;
• documents the implementation lineage and composition relationship;
• states explicitly that this implementation composes aset-python-sqlite as its Seed layer and does not fork, replace, or redefine Seed resolution semantics;
• rebuilds MANIFEST.json.

No upstream binding, canon identity, conformance target, network semantics, runtime behavior, protocol, or implementation logic is changed.

Validation

Validated against the exact immutable upstream identities:

• ASET Seed commit 633c130187b2a2bb42f24cfd66662d475de385d2
• aset-python-sqlite commit daee6da46636ce4996cf1b880d1adbb6b36e1996
• ASET Network Extension commit e15c88e060e1b2c129e97a003fdc5385e1b63a71

Results include:

• CROSS_BINDING_SEED_IDENTITY=MATCH
• IMPLEMENTATION_EXTENSION_RELATION=ADDITIVE
• UPSTREAM_LOCK_VERIFICATION=PASS
• base PYTHON_SQLITE_PROFILE_GATE=PASS
• NETWORK_CONFORMANCE=18/18 PASS
• NETWORK_CONFORMANCE_CASE_HASHES=PASS
• SOURCE_ARCHIVE_DETERMINISM=PASS
• WHEEL_BUILD=PASS
• BLACKBOX_RELEASE_AUDIT=PASS
• DOCKER_TLS=PASS
• DOCKER_SIGNED_TRANSPORT=PASS
• DOCKER_REMOTE_IMPORT_FAIL_CLOSED=PASS
• DOCKER_TARGET_LOCAL_SEED_RESOLUTION=PASS
• DOCKER_EFFECT_BOUNDARY=PASS
• DOCKER_TWO_NODE_GATE=PASS
• NETWORK_PYSQL_PROFILE_GATE=PASS