Add relationship patterns functionality

Add relationship properties functionality

Update API

Add multihop search support

Add smart search to sdk

- Direct mode routes every SDK call to a standalone rushdbd; Cloud-only
  methods raise CloudOnlyError, unstageable transaction writes raise
  DirectModeError, before anything is sent.
- Transactions stage creates, update, set, delete_by_id, attach and
  imports; detach without a type removes every type both ways.
- Keyword search (records.text_search), text indexes (db.text_indexes),
  hybrid vector search options, search meta on results.
- Breaking: records.find raises instead of returning an empty result;
  ImportsAPI (import runs/uploads, no server) removed.
- Fixed: find_by_id of several ids, export route, import_* when
  returnResult is off.
- Version 3.0.0.

From 3.0 the self-hostable part of RushDB is the engine (rushdbd), reached
in direct mode. The dashboard, managed embeddings and the AI features are
part of RushDB Cloud. Remove the remaining mentions of a self-hosted
platform: mode tables, the `url` option (a RushDB Cloud API endpoint),
RUSHDB_API_URL, and the traversal notes (an omitted hops.max means up to
10 hops; there is no unbounded traversal).

- The SDK has no runtime dependencies: it never imported `requests` or
  `python-dotenv` (the client uses urllib), so installing it no longer
  pulls in requests/urllib3/idna. python-dotenv moves to the dev group
  (the test setup loads .env); types-requests is dropped.
- Dev tooling raised to patched releases: black >= 26.3.1,
  pytest >= 9.0.3, Pygments >= 2.20.0, python-dotenv >= 1.2.2.
- requires-python >= 3.10 (3.8 and 3.9 are end-of-life, and the patched
  tools need 3.10); CI matrix 3.10-3.13. ruff stays on 0.12.x so the
  upgrade does not change the lint rule set.
- One dev dependency list ([dependency-groups]); the duplicate
  `dev` extra is removed.

Closes Dependabot alerts 5-9, 11-19 (urllib3, requests, idna,
python-dotenv, black, pytest, Pygments).

feat!: 3.0 — RushDB Cloud and self-hosted engine (direct mode)