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>

home_assistant/packages/el512_panel.yaml

@@ -0,0 +1,133 @@
+# Helper sensors for the EL512.256-H ESPHome display (esphome/el512-panel.yaml).
+#
+# Install: put this file in /config/packages/ and make sure configuration.yaml has
+#
+#   homeassistant:
+#     packages: !include_dir_named packages
+#
+# then restart Home Assistant. All lists use the same compact text format so the
+# ESP32 can split them cheaply: fields separated by "|", entries by ";".
+
+template:
+  # Forecast and agenda come from actions, so they refresh on a timer.
+  - triggers:
+      - trigger: time_pattern
+        minutes: "/15"
+      - trigger: homeassistant
+        event: start
+      - trigger: event
+        event_type: event_template_reloaded
+    actions:
+      - action: weather.get_forecasts
+        target:
+          entity_id: weather.knmi_home
+        data:
+          type: daily
+        response_variable: fc
+      - action: calendar.get_events
+        target:
+          entity_id:
+            - calendar.mangavalk_gmail_com
+            - calendar.li_s_happy_home
+            - calendar.feestdagen_in_nederland
+        data:
+          duration:
+            days: 14
+        response_variable: cal
+    sensor:
+      # days: "Sun|cloudy|12|11|0;Mon|partlycloudy|14|10|20;..."
+      #        weekday|condition|high|low|rain chance %
+      - name: EL512 forecast
+        unique_id: el512_forecast
+        icon: mdi:weather-partly-cloudy
+        state: "{{ fc['weather.knmi_home'].forecast | count }}"
+        attributes:
+          days: >-
+            {%- set ns = namespace(out=[]) -%}
+            {%- for d in fc['weather.knmi_home'].forecast[:7] -%}
+              {%- set ns.out = ns.out + [
+                    (as_datetime(d.datetime) | as_local).strftime('%a') ~ '|' ~
+                    d.condition ~ '|' ~
+                    (d.temperature | round(0) | int) ~ '|' ~
+                    (d.templow | default(d.temperature) | round(0) | int) ~ '|' ~
+                    (d.precipitation_probability | default(0) | int)] -%}
+            {%- endfor -%}
+            {{ ns.out | join(';') }}
+
+      # events: "Mon 19|11:00|Work;Tue 20||Holiday;..."
+      #          day|start time (empty = all day)|title
+      - name: EL512 agenda
+        unique_id: el512_agenda
+        icon: mdi:calendar
+        state: >-
+          {%- set ns = namespace(n=0) -%}
+          {%- for c in cal.values() -%}{%- set ns.n = ns.n + c.events | count -%}{%- endfor -%}
+          {{ ns.n }}
+        attributes:
+          events: >-
+            {%- set ns = namespace(ev=[]) -%}
+            {%- for c in cal.values() -%}
+              {%- for e in c.events -%}{%- set ns.ev = ns.ev + [e] -%}{%- endfor -%}
+            {%- endfor -%}
+            {%- set out = namespace(items=[]) -%}
+            {%- for e in (ns.ev | sort(attribute='start'))[:10] -%}
+              {%- if e.start | length == 10 -%}
+                {%- set day = strptime(e.start, '%Y-%m-%d').strftime('%a %d') -%}
+                {%- set time = '' -%}
+              {%- else -%}
+                {%- set t = as_datetime(e.start) | as_local -%}
+                {%- set day = t.strftime('%a %d') -%}
+                {%- set time = t.strftime('%H:%M') -%}
+              {%- endif -%}
+              {%- set title = (e.summary | default('')) | replace('|', '/') | replace(';', ',') -%}
+              {%- set out.items = out.items + [day ~ '|' ~ time ~ '|' ~ title[:40]] -%}
+            {%- endfor -%}
+            {{ out.items | join(';') }}
+
+  # Whatever media player is playing right now; position advances every 5 s.
+  - triggers:
+      - trigger: time_pattern
+        seconds: "/5"
+    sensor:
+      - name: EL512 now playing
+        unique_id: el512_now_playing
+        icon: mdi:play-circle
+        state: >-
+          {%- set p = states.media_player | selectattr('state', 'eq', 'playing') | list -%}
+          {{ p[0].entity_id if p else 'idle' }}
+        attributes:
+          # "title|artist|album|player|position s|duration s"
+          info: >-
+            {%- set p = states.media_player | selectattr('state', 'eq', 'playing') | list -%}
+            {%- if p -%}
+              {%- set a = p[0].attributes -%}
+              {%- set pos = a.media_position | default(0) -%}
+              {%- if a.media_position_updated_at is defined and a.media_position_updated_at -%}
+                {%- set pos = pos + (now() - as_datetime(a.media_position_updated_at)).total_seconds() -%}
+              {%- endif -%}
+              {%- set dur = a.media_duration | default(0) -%}
+              {%- set pos = [pos, dur] | min if dur else pos -%}
+              {{ [a.media_title | default(a.app_name | default('')), a.media_artist | default(a.media_series_title | default('')),
+                  a.media_album_name | default(''), a.friendly_name | default(''), pos | int, dur | int]
+                 | map('string') | map('replace', '|', '/') | join('|') }}
+            {%- endif -%}
+
+  # Plex: the server sensor has one attribute per stream ("user - client": "title").
+  - sensor:
+      - name: EL512 Plex streams
+        unique_id: el512_plex_streams
+        icon: mdi:plex
+        state: "{{ states('sensor.mangavalkserver') }}"
+        attributes:
+          # "user - client|title;..."
+          streams: >-
+            {%- set s = states.sensor.mangavalkserver -%}
+            {%- set ns = namespace(out=[]) -%}
+            {%- if s -%}
+              {%- for k, v in s.attributes.items()
+                    if k not in ['unit_of_measurement', 'friendly_name', 'icon', 'device_class', 'state_class'] -%}
+                {%- set ns.out = ns.out + [(k | replace('|', '/') | replace(';', ',')) ~ '|' ~
+                                           (v | string | replace('|', '/') | replace(';', ','))] -%}
+              {%- endfor -%}
+            {%- endif -%}
+            {{ ns.out | join(';') }}