Rebrand to DSSH + comprehensive README + sanitize defaults

- New top-level README in 中文 covering install (.cia / .3dsx /
  3dslink), server-side RSA setup, config.ini, full physical-key
  table, soft keyboard pages, IME usage (full pinyin + abbreviation
  + prefix fallback), debug page, source build, project layout,
  architecture diagram, and credits.
- Old M0 README replaced (was talking about docker / Azahar /
  un-shipped milestones).
- Add MIT LICENSE with notes on bundled third-party licenses
  (Zpix OFL, rime-ice LGPL, libssh2 BSD, mbedTLS Apache, etc).
- Sanitize the user's actual server IP out of config.ini.example,
  sd_template/README.md, source/config.c default, and
  source/config.h docstring — replaced with
  your-server.example.com placeholder.
- sd_template/README.md trimmed: M1-era key bindings (X = swkbd,
  L = Ctrl-C, etc) replaced with a pointer to the project README.

Author: exdekotive

LICENSE

@@ -0,0 +1,34 @@
+MIT License
+
+Copyright (c) 2026 exdekotive
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+Note: This license covers the original DSSH source code only.  Bundled or
+referenced third-party components retain their own licenses:
+
+  - Zpix font: SIL OFL 1.1
+  - Terminus font: SIL OFL 1.1
+  - rime-ice dictionary: LGPL-3.0
+  - libssh2: BSD-3-Clause
+  - mbedTLS: Apache-2.0
+  - libctru / citro2d / citro3d: zlib / various
+  - skmtrd/3dssh-derived terminal/UTF-8/renderer code: MIT
+
+When redistributing the .cia or .3dsx, please respect those licenses.