Fix the visualisers, add a notification icon, bump to v0.11.6 / android-v0.11.5

[Shik3i]

Why the web visualiser looked dead

It carried three mis-tunings that the Android client had already diagnosed and fixed. Each one is described in Android's own source comments; none was ported back.

	Android (tuned)	Web (was)	Android's comment
FFT size	2048	1024	"at 512 the bins are 86 Hz apart — wider than the bottom third of a log-spaced display, so those bands collapse onto each other and eighteen bars end up drawing the same number"
dB window	−78 … −4	never set (defaults −100 … −30)	"the ceiling was −14, which ordinary mastered speech passes for most of a sentence: nearly every band pinned at full height"
Tilt	0.8	1.6	"at 1.6 the top bands were lifted by 2.6x and clipped on their own"

A clipped bar cannot move. At 43 Hz per bin the lowest dozen bars draw the same number. That is the "only the first 10% moves, the rest is static" report.

What both clients were missing

Normalisation against what the display has been hearing, rather than against full scale. It is why a quietly mastered episode drew a flat display while a loud one drew a lively one — and podcast audio makes this worse than music does, because levelling between shows is far less consistent. Bounded on both ends: never more than 3×, and never lifts silence, so a pause stays empty instead of becoming a wall of room tone.

Measured, not asserted

Run in a real browser against a synthetic voice (harmonics + sibilance), old configuration vs new, 120 frames, average peak-to-trough movement per band:

                   low bands   top bands
before                 0.783       1.000
after                  0.942       0.465

The top bands were not static in the old configuration — they were slamming between the rails, which reads as noise rather than as a spectrum. The bottom third moved less than it does now.

Counter-evidence, included deliberately: an earlier run against a source with no content above 1.7 kHz showed the opposite for the top bands (before 0.559, after 0.104). The reason is that the old settings were amplifying the noise floor into something that looked like signal, and the new window correctly reports an empty band as empty. I am reporting both numbers rather than the flattering one.

The mapping moved to lib/audio/spectrum.ts so it can be tested without a browser. That is also how the tilt regression is pinned: restoring 1.6 makes more than a third of the bands clip on a speech-shaped input and fails the test — verified by putting the old value back.

The notification icon

New-episode notifications used android.R.drawable.stat_sys_download_done — a download tick, for something that is not a download. There was no suitable glyph in the project, so this adds one.

The feed mark rather than a bell: it is what "new items in a show you follow" means, and it survives 24dp in a status bar where a bell's clapper and shoulders do not. Built from exact geometry (a dot plus two annular quarter-sectors sharing an origin) rather than traced by hand, and checked by rasterising the paths before wiring it in. Confirmed compiled into the APK via aapt2 dump resources.

Verification

• Web: 155 tests, svelte-check clean, translations/docs/release-policy gates pass.
• Android: testDebugUnitTest and testReleaseUnitTest both green — the two tasks the release workflow runs.
• On an emulator: playback runs with the new gain stage on the audio thread with no crash and no audio-track error.

Versions

apps/web → 0.11.6, Android → versionCode 45 / 0.11.5. This also carries the audit fixes merged in #25, which have not been in a release yet.

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