feat: rework audio engine, simplify UI, add CI

.github/workflows/build.yml

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+name: build firmware
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+  workflow_call:
+    inputs:
+      release_tag:
+        description: "If set, upload the built .uf2 files to this release tag"
+        type: string
+        required: false
+        default: ""
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        kit:
+          - { name: trippy,    flag: "" }
+          - { name: 80s,       flag: "-DCHAMBORD_KIT_80S" }
+          - { name: angularj,  flag: "-DCHAMBORD_KIT_ANGULARJ" }
+          - { name: mix,       flag: "-DCHAMBORD_KIT_MIX" }
+          - { name: tekke,     flag: "-DCHAMBORD_KIT_TEKKE" }
+          - { name: acoustic3, flag: "-DCHAMBORD_KIT_ACOUSTIC3" }
+        enc:
+          - { dir: "1",  suffix: "" }                    # normal encoder
+          - { dir: "-1", suffix: ".encoder_reversed" }   # reversed encoder
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install arduino-cli
+        uses: arduino/setup-arduino-cli@v2
+
+      - name: Install RP2350 core and libraries
+        run: |
+          arduino-cli config init --additional-urls https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
+          arduino-cli core update-index
+          arduino-cli core install rp2040:rp2040@5.6.1
+          arduino-cli lib install \
+            RotaryEncoder@1.5.3 \
+            Bounce2@2.71.0 \
+            RPi_Pico_TimerInterrupt@1.3.1
+
+      - name: Build ${{ matrix.kit.name }}${{ matrix.enc.suffix }}
+        run: |
+          arduino-cli compile \
+            -b rp2040:rp2040:rpipico2:freq=276,opt=Optimize3 \
+            --build-property "compiler.cpp.extra_flags=-DCHAMBORD_ENC_DIR=${{ matrix.enc.dir }} ${{ matrix.kit.flag }}" \
+            --output-dir out \
+            firmware/Pikobeats
+          mv out/Pikobeats.ino.uf2 "Pikobeats.${{ matrix.kit.name }}${{ matrix.enc.suffix }}.rp2350.uf2"
+
+      # Downloadable from the Actions run for every commit
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: Pikobeats.${{ matrix.kit.name }}${{ matrix.enc.suffix }}.rp2350
+          path: Pikobeats.${{ matrix.kit.name }}${{ matrix.enc.suffix }}.rp2350.uf2
+
+      # When called from the release workflow, attach the binaries to the release
+      - name: Upload to release
+        if: ${{ inputs.release_tag != '' }}
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release upload "${{ inputs.release_tag }}" \
+            "Pikobeats.${{ matrix.kit.name }}${{ matrix.enc.suffix }}.rp2350.uf2" --clobber

.github/workflows/release-please.yml

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+name: release-please
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    outputs:
+      release_created: ${{ steps.rp.outputs.release_created }}
+      tag_name: ${{ steps.rp.outputs.tag_name }}
+    steps:
+      - uses: googleapis/release-please-action@v4
+        id: rp
+
+  # On a new release, build every kit (normal + reversed encoder) and attach
+  # the .uf2 files to the release.
+  firmware:
+    needs: release-please
+    if: ${{ needs.release-please.outputs.release_created == 'true' }}
+    uses: ./.github/workflows/build.yml
+    with:
+      release_tag: ${{ needs.release-please.outputs.tag_name }}

.release-please-manifest.json

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+{
+  ".": "0.0.0"
+}

README.md

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 # Chambord
 
-Chambord is a eurorack module, using the RP2040 or 2350 to implement a sampler.
+Chambord is a eurorack module, using the RP2040 or 2350 to implement an
+8-channel trigger-in drum sampler.
 
-# UI
+The 8 channels are laid out **top to bottom = channel 1 to 8**. Each channel
+has a trigger input jack and a bicolor (red/green) LED. There is one encoder
+(turn + press) and one CV input.
 
-The ui is controlled via the encoder and encoder button. The feedback is the color of the current selected track or track 7.
+# How to use it
 
-1. In the default mode (0) turning the encoder selects the current track to work on. It will blink orange from default green.
-2. Press the encoder button (short press) once, enter mode 1 to change the pitch of the current track.
-3. Press the encoder again (short press) to enter mode 2, to change the sample. Each track has 4 samples associated with it.
-5. Hold the ecoder buton for 1/2 a second (say 'one') and you assign the CV input to modulate the volume of the current track.
+There are only two controls: **turn** the encoder and **press** the encoder.
 
-That's about it.
+## Turning the encoder
+
+What turning does depends on the current "page". You step through the pages by
+**short-pressing** the encoder:
+
+```
+press        press         press        press
+SELECT  -->  SAMPLE  -->  VOLUME  -->  PITCH  --> (back to SELECT)
+```
+
+- **SELECT** (start here): turn to choose the channel you want to work on.
+- **SAMPLE**: turn to change the sample on the selected channel. Each channel
+  has 4 samples (banks A–D); turning steps between them.
+- **VOLUME**: turn to change the volume of the selected channel.
+- **PITCH**: turn to change the pitch of the selected channel.
+
+A short press always advances to the next page and wraps back to SELECT.
+
+## Reading the LEDs
+
+While you're editing, only the **selected channel's** LED lights, colour-coded
+by page (green = choosing a thing, amber = setting an amount):
+
+| LED              | Page                                  |
+|------------------|---------------------------------------|
+| green steady     | SELECT  (turn to pick the channel)    |
+| green blinking   | SAMPLE  (turn to change the sample)   |
+| amber steady     | VOLUME  (turn to change the volume)   |
+| amber blinking   | PITCH   (turn to change the pitch)    |
+
+You'll also hear sample/volume/pitch changes as you turn.
+
+## Screensaver / trigger activity
+
+When you haven't touched the encoder for about **10 seconds**, the row switches
+to a trigger-activity display: every channel flashes **green** when it gets a
+trigger. Touch the encoder and it goes back to showing what you're editing.
+(This keeps trigger flashes from distracting you while you work.)
+
+## CV input
+
+**Long-press** the encoder (hold ~3/4 second) to assign the CV input to the
+**volume** of the currently selected channel. Long-press again on the same
+channel to turn CV off.
+
+## Settings are saved
+
+Your per-channel sample and pitch choices (and the CV assignment) are saved
+automatically to flash a moment after you stop adjusting, and restored on the
+next power-up. Saving only happens while nothing is sounding, so it never
+interrupts playback.
+
+## If the encoder turns the wrong way
+
+Open `firmware/Pikobeats/Pikobeats.ino` and change `ENCODER_DIR` from `1` to
+`-1` (near the top), then rebuild.