ESPHome external component for Samsung 2x20 serial VFD

Component (components/samsung_vfd), example device config, README and
CLAUDE.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

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+# CLAUDE.md
+
+ESPHome external component for a Samsung 2×20 serial VFD (5 V TTL, 9600 8N1,
+write-only). It is consumed from git by an ESPHome server through
+`external_components: source: github://...`, so the layout must stay
+`components/samsung_vfd/` at the repo root.
+
+## Layout
+
+- `components/samsung_vfd/__init__.py`: config schema, codegen and the action
+  registrations (`print`, `printf`, `clear`, `home`).
+- `components/samsung_vfd/samsung_vfd.h`: the class, the control-byte constants
+  and the templated action classes.
+- `components/samsung_vfd/samsung_vfd.cpp`: the shadow buffer, word wrap,
+  UTF-8 → single-byte sanitising and `flush_()`.
+- `examples/samsung-vfd.yaml`: the full reference device config. It pulls the
+  component from GitHub; for local work, switch to the commented
+  `type: local, path: ../components` source.
+
+## Design rules
+
+- `lines_` is the screen as it should be, each line padded to exactly `cols_`.
+  Every change goes through `flush_()`. It rebuilds the payload, returns early
+  if the payload equals `last_payload_`, and otherwise sends `0B` (home) plus
+  the payload. Don't clear before redrawing: that causes flicker.
+- Anything that changes the display out of band (clear, init) must reset
+  `last_payload_` so the next flush retransmits.
+- Text sent to the display is one byte per character; always pass it through
+  `sanitize_()`.
+- Keep the protocol constants in `samsung_vfd.h`. Only `ESC @`, `0C` and `0B`
+  are known to work.
+
+## Checking changes
+
+Hardware isn't available to Claude, so validate with ESPHome itself:
+
+```
+pip install esphome
+cd examples
+# switch external_components to the local source first
+esphome config samsung-vfd.yaml     # schema check
+esphome compile samsung-vfd.yaml    # full C++ build
+```
+
+`secrets.yaml` is gitignored. Copy `examples/secrets.yaml.example` to
+`examples/secrets.yaml` to compile.
+
+Follow ESPHome C++ style: `this->` on members, a trailing `_` on protected
+members, and the `esphome::samsung_vfd` namespace.