feat(analysis): attenuation, fermentation curves and brew timings

Adds the analysis page the old app never had: how consistently the brews
ferment, and how long each one takes.

What it shows
-------------
- **Attenuation by brew** - what fraction of the original gravity was
  fermented away, for every finished brew.
- **Fermentation curves** - the typical shape of a fermentation, drawn as a
  median curve with the min-max envelope behind it. Plotting every brew
  individually gave 16 near-identical lines and an unreadable legend.
- **Every finished brew** - OG, FG, ABV, attenuation, days in the fermenter,
  days to reach 1.010, and the finish date.
- **Readings that need a second look** - readings outside the plausible
  hydrometer range.
- Headline figures: average attenuation and its spread, average brew time,
  average time to 1.010.

Data quality
------------
One live run (run 12) has a final gravity of 900, which worked out as 338%
attenuation and dragged the average to 103.2%. That is not a real result,
so:

- Attenuation is rejected when the final gravity is not physically possible
  for the original gravity.
- Runs that fail that check are EXCLUDED from the averages rather than
  silently distorting them, and are listed on the page as needing review.
- The average now reads 87.5% +/- 7.4 percentage points across 16 brews.

Chart bugs found while building this
------------------------------------
- **The gravity charts had their y axis reversed.** With `reverse: true`
  the high reading sits at the BOTTOM, so the fermentation curve climbed
  left to right - it read as gravity *rising* as the beer fermented. A
  brewer reads a fermentation as a descending line. The point-scale run
  chart on the run detail page had the same bug. Both are fixed.
- **The curve chart's x axis was treated as categorical.** The x values are
  numeric (0-100), and Chart.js defaults a line chart's x axis to
  category, which collapsed every point onto index 0 and rendered the
  curve as a sliver at the origin. The axis is now explicitly linear.
- **The curve was interpolated by exact key lookup**, so it only worked when
  every brew happened to be read at the same progress points. It now
  interpolates between a brew's actual readings, and the curve carries 21
  points across the full range.
- **Long beer names were clipped** at the left edge of the attenuation
  chart ("...x crying out loud"). Names are trimmed to 18 characters with
  an ellipsis; the tooltip and the table carry the full name.

Tests
-----
127 (up from 105). The two chart regressions are covered by reading
`charts.js` and asserting the gravity axis is not reversed and that long
names are trimmed - these are exactly the kind of change that silently
reverts, and they are invisible to a screenshot test.

src/flask/templates/base.html

@@ -23,6 +23,8 @@
                href="{{ url_for('analysis.active') }}">Active Beers</a>
             <a class="nav__link {% if current_path == '/history' %}is-active{% endif %}"
                href="{{ url_for('analysis.history') }}">History</a>
+            <a class="nav__link {% if current_path == '/analysis' %}is-active{% endif %}"
+               href="{{ url_for('analysis.deep') }}">Analysis</a>
         </nav>
 
         <form method="post" action="{{ url_for('auth.logout') }}" class="topbar__logout">