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/examples/squaring_bot.py

@@ -0,0 +1,52 @@
+"""Squaring bot — replies to every number with its square.
+
+Run with the simplex-chat package installed:
+
+    python examples/squaring_bot.py
+
+Sends `n * n = ...` for any text message that parses as a number; falls
+back to a hint for non-number messages; responds to `/help` with usage.
+"""
+
+from __future__ import annotations
+
+import re
+
+from simplex_chat import (
+    Bot,
+    BotCommand,
+    BotProfile,
+    Message,
+    ParsedCommand,
+    SqliteDb,
+    TextMessage,
+)
+
+bot = Bot(
+    profile=BotProfile(display_name="Squaring bot"),
+    db=SqliteDb(file_prefix="./squaring_bot"),
+    welcome="Send me a number, I'll square it.",
+    commands=[BotCommand(keyword="help", label="Show help")],
+)
+
+NUMBER_RE = re.compile(r"^-?\d+(\.\d+)?$")
+
+
+@bot.on_message(content_type="text", text=NUMBER_RE)
+async def square(msg: TextMessage) -> None:
+    n = float(msg.text or "0")
+    await msg.reply(f"{n} * {n} = {n * n}")
+
+
+@bot.on_message(content_type="text")
+async def fallback(msg: Message) -> None:
+    await msg.reply("Send me a number, like 7 or 3.14.")
+
+
+@bot.on_command("help")
+async def help_cmd(msg: Message, _cmd: ParsedCommand) -> None:
+    await msg.reply("Send a number, I'll square it.")
+
+
+if __name__ == "__main__":
+    bot.run()