simplex-chat-python: add python library (#6954)

* docs: simplex-chat-python design and implementation plan

* bots: Python wire types codegen

* simplex-chat-python: package scaffold

* simplex-chat-python: native libsimplex loader

* simplex-chat-python: async FFI wrappers

* simplex-chat-python: ChatApi with 49 api methods

* simplex-chat-python: Bot class with decorators and dispatch

* simplex-chat-python: install CLI, example bot, README

* simplex-chat-python: audit fixes

* bots: regenerate API docs and types

Catches up the markdown, TypeScript and Python codegen outputs with two
upstream schema changes:

- APIConnectPlan.connectionLink became optional (from sh/python-lib audit
  fixes); cmdString and EBNF syntax now reflect optional parameter.
- APIAddGroupRelays command and CRGroupRelaysAdded/CRGroupRelaysAddFailed
  responses added in #6917 (relay management). The TS and markdown outputs
  were regenerated when #6917 landed but the Python types module only got
  the new entries with this regeneration.

* core: refresh SQLite query plans after relay_inactive_at migration

The M20260507_relay_inactive_at migration (#6917 / #6952) shifted the
query plans that 'Save query plans' verifies. Regenerated via the test
that owns those snapshots; no behavioral change.

* bots: keep APIConnectPlan connectionLink as required parameter

The prior audit-fixes commit changed the syntax expression to `Optional ...`
because the Haskell field is `connectionLink :: Maybe AConnectionLink`.
That misrepresents the API contract: the `Maybe` is purely an internal
signal for link-parsing failure (the handler returns `CEInvalidConnReq`
on `Nothing`), not API-level optionality. Callers MUST always pass a
connection link.

Revert the syntax expression to `Param "connectionLink"` and add a
comment so the intent is preserved next time someone audits.

Regenerates COMMANDS.md, commands.ts and _commands.py to match.

packages/simplex-chat-python/src/simplex_chat/__main__.py

@@ -0,0 +1,35 @@
+"""CLI: ``python -m simplex_chat install [--backend=sqlite|postgres]``."""
+
+from __future__ import annotations
+
+import argparse
+import sys
+
+from . import _native
+
+
+def main(argv: list[str] | None = None) -> int:
+    p = argparse.ArgumentParser(prog="simplex_chat")
+    sub = p.add_subparsers(dest="command", required=True)
+    install = sub.add_parser("install", help="Pre-fetch libsimplex into the user cache")
+    install.add_argument(
+        "--backend",
+        choices=["sqlite", "postgres"],
+        default="sqlite",
+        help="which libsimplex variant to download (default: sqlite)",
+    )
+    args = p.parse_args(argv)
+    # `args.command` is always set: `add_subparsers(required=True)` makes
+    # argparse exit before reaching this point if no subcommand is given.
+    assert args.command == "install"
+    try:
+        path = _native._resolve_libs_dir(args.backend)
+        print(f"libsimplex installed at: {path}")
+        return 0
+    except Exception as e:
+        print(f"install failed: {e}", file=sys.stderr)
+        return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())