Give walks the two sleep pattern views

Walks had the overview tile, the window list and minutes per day, but not the
two views that answer the questions sleep already answers: when in the day does
it actually happen, and is today keeping up.

"When … walks" is the sleep actogram drawn from walk windows, so the drawing
moves into drawActogram(svgId, windows, barCls) and both timelines become one
line each. Nothing about that picture was ever sleep-specific — it clips
windows to day rows and shades them — so the third caller costs nothing.

"Walk trend" is the sleep trend's shape with three deliberate differences.
Today and yesterday are built from their own walk boundaries rather than hourly
samples, so the steps stay square: a 30-minute walk is a step, not an hour-wide
ramp. The average keeps hourly sampling, since a mean over many days is a
smooth reference with no steps of its own to preserve. And there is no
projected tail — sleep is a state the puppy drifts back into, so continuing
today's line by what the average day adds is a fair guess, while walks are
decisions, and projecting them would be predicting the handler, not the dog.

The goal is a line, not a band: the five-minute rule gives one number to reach
with no upper bound a band would imply. With no projection to carry it, the ✓
that marks being on track goes on today's own chip.

The axis stays linear where the sleep trend stretches above 10h. That stretch
exists because sleep's interesting hours crowd a 16h goal; a walk total reads
the same at 10 minutes as at 60.

Both panels sit with the other walk views rather than beside their sleep twins,
following the grouping-by-subject the charts just moved to, and both hide
themselves until a walk exists so they cost nothing to anyone not logging them.

src/index.html

@@ -243,6 +243,27 @@
         </div>
       </section>
 
+      <!-- The two walk patterns mirror the sleep ones below, drawn from walk
+           windows instead of sleep windows. Both stay hidden until there is a
+           walk to draw, so they cost nothing to anyone not tracking walks. -->
+      <section class="patterns" data-panel="walk-timeline" hidden>
+        <h2><span id="walk-timeline-title">When walking</span> <span class="muted-note" data-chart-days-label>(last 7 days)</span></h2>
+        <svg id="chart-walk-timeline" class="chart-svg" viewBox="0 0 320 125" role="img" aria-label="Walks per day"></svg>
+        <p class="muted-note">Each row is a day, midnight to midnight; shaded = out on a walk. Tap a row to open that day.</p>
+      </section>
+
+      <section class="patterns" data-panel="walk-trend" hidden>
+        <h2>Walk trend</h2>
+        <svg id="chart-walk-trend" class="chart-svg" viewBox="0 0 320 180" role="img" aria-label="Cumulative minutes walked through the selected day, the day before it, the recent average, and the age-based daily goal"></svg>
+        <div class="legend">
+          <span class="lg wtrend-today"><span class="sw"></span><span id="legend-wtrend-today-text">Today</span></span>
+          <span class="lg wtrend-yesterday" id="legend-wtrend-yesterday"><span class="sw"></span><span id="legend-wtrend-yesterday-text">Yesterday</span></span>
+          <span class="lg wtrend-avg" id="legend-wtrend-avg"><span class="sw"></span><span id="legend-wtrend-avg-text">7-day avg</span></span>
+          <span class="lg wtrend-goal" id="legend-wtrend-goal" hidden><span class="sw"></span><span id="legend-wtrend-goal-text">Goal</span></span>
+        </div>
+        <p class="muted-note">Minutes walked so far at each point of the day, against yesterday and the average over the picked window. The line climbs only while a walk is on, so every step is one walk.</p>
+      </section>
+
       <!-- The day-window picker lives in this panel but governs every
            day-window chart on the page — the training grid above, both sleep
            patterns below, the counts panel and the walk chart — so changing it