Add ESPHome display component; ring-buffer driver shared with PlatformIO

Driver (components/el512/el512_panel.*, ESP-IDF only):
- DMA ring of 8 x 4 lines (17 KB) refilled from the I2S EOF interrupt
  (IRAM) instead of a 142 KB full-frame stream; ~107 KB heap freed.
- 256-entry lookup table encodes 8 pixels per step.
- Back buffer + displayed buffer, swapped at the start of a frame.
- PlatformIO builds it via lib_extra_dirs (EL512Core); lib/EL512 keeps
  the Adafruit GFX front end.

ESPHome external component (platform: el512):
- DisplayBuffer with optional ENABLE / _LOWPWR pins, set_enabled(),
  set_low_power(), helper functions for page lambdas.
- still_alive_page: plays the Portal end-credits show, then returns to
  the previous page.

Still Alive engine moved to components/el512/still_alive.* with a built-in
5x7 font (from Adafruit GFX, BSD); the PlatformIO demo uses the same code.
The importer writes components/el512/still_alive_data.h and stops at 200 s
(--until-ms), matching the hand-trimmed data.

esphome/el512-panel.yaml: 8 pages (clock, forecast, agenda, dashboard,
now playing, Plex, solar, Still Alive), page select, rotation, display
and low-power switches, message text. home_assistant/packages/el512_panel.yaml:
helper template sensors for forecast, agenda, now playing and Plex streams.

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

components/el512/still_alive.h

@@ -0,0 +1,110 @@
+// Portal-style end-credits show for the EL512.256-H: timed song text typed into
+// a console on the left, credits typed top right, ASCII art bottom right.
+//
+// Framework-agnostic: draws straight into an EL512Panel with the built-in 5x7
+// font, so the PlatformIO demo (src/still_alive) and the ESPHome component use
+// the same code. The content is in still_alive_data.h, generated by
+// tools/import_still_alive.py.
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+class EL512Panel;
+
+namespace el512sa {
+
+enum : uint8_t {
+  STEP_NEWLINE = 1 << 0,  // start a new line after the text is typed
+  STEP_CLEAR = 1 << 1,    // clear the console before typing
+};
+
+// One timed piece of console text. Steps are sorted by startMs.
+struct LyricStep {
+  uint32_t startMs;  // from the start of the show
+  uint16_t durMs;    // the text is typed out evenly over this time
+  uint8_t flags;
+  int8_t art;  // picture to show (index into ARTS), or ART_KEEP
+  const char *text;
+};
+
+struct Art {
+  const char *const *lines;
+  uint8_t count;
+};
+
+static constexpr int8_t ART_KEEP = -1;  // leave the current picture
+static constexpr int8_t ART_NONE = 0;   // ARTS[0] is always the empty picture
+
+// Fixed-size character console in the 5x7 font (6x8 cells), optionally inside a
+// dashed frame. Text wraps at the right edge and scrolls up past the bottom row.
+class TextBox {
+ public:
+  static constexpr uint8_t MAX_COLS = 48;
+  static constexpr uint8_t MAX_ROWS = 32;
+  static constexpr int16_t PAD = 4;
+  static constexpr int16_t CHAR_W = 6;
+  static constexpr int16_t CHAR_H = 8;
+
+  TextBox(int16_t x, int16_t y, int16_t w, int16_t h);
+
+  uint8_t cols() const { return cols_; }
+  uint8_t rows() const { return rows_; }
+
+  void clear();
+  void put(char c);
+  void print(const char *s);
+  void draw(EL512Panel &panel, bool cursor, bool frame = true) const;
+
+ private:
+  void newLine();
+
+  int16_t x_, y_, w_, h_;
+  uint8_t cols_, rows_;
+  uint8_t row_ = 0, col_ = 0;
+  char text_[MAX_ROWS][MAX_COLS + 1];
+};
+
+class StillAlivePlayer {
+ public:
+  static constexpr uint32_t START_DELAY_MS = 1000;  // after start()
+  static constexpr uint32_t CURSOR_BLINK_MS = 300;
+  static constexpr uint32_t HOLD_MS = 10000;  // after the last step, before finished()
+
+  StillAlivePlayer();
+
+  // Restart the show; it begins START_DELAY_MS after nowMs.
+  void start(uint32_t nowMs);
+  // Advance to nowMs; true if the screen changed (text, picture or cursor).
+  bool update(uint32_t nowMs);
+  // Draw the whole show; the caller clears the panel first and shows it after.
+  void draw(EL512Panel &panel) const;
+  // True once the last step has been typed and HOLD_MS has passed.
+  bool finished(uint32_t nowMs) const;
+  // When to start the music, relative to start().
+  static uint32_t songStartMs();
+
+ private:
+  bool updateLyrics(uint32_t t, uint32_t nowMs);
+  bool updateCredits(uint32_t t);
+  void showArt(int8_t id);
+
+  TextBox lyrics_;
+  TextBox credits_;
+  TextBox art_;
+  uint32_t showStart_ = 0;
+  size_t step_ = 0;
+  size_t charIdx_ = 0;
+  bool stepStarted_ = false;
+  bool done_ = false;
+  uint32_t doneAt_ = 0;
+  size_t creditIdx_ = 0;
+  size_t creditChar_ = 0;
+  bool creditLineOpen_ = false;
+  bool creditsDone_ = false;
+  uint32_t creditLineAt_ = 0;
+  bool cursor_ = false;
+  bool creditsCursor_ = false;
+};
+
+}  // namespace el512sa