docs(cadecon): align tutorials with convergence / palette / fit-mode changes

[daharoni]

Final item of the pre-publication review series: bring the in-app CaDecon tutorials in line with the behavior shipped in #153–163. Content + figure-color changes only — verified with tsc -b apps/cadecon, eslint, and prettier.

What changed

Theory — "How does CaDecon know when to stop?" (03-theory.ts step 11)
The step carried an explicit NOTE that the stop criterion was "still being finalized." It's now finalized, so I removed the note and rewrote the description to match: convergence is judged in kernel shape space — stability of the rise-to-peak time and FWHM — declared after several consecutive stable iterations, with the reported kernel = the median (consensus) of the last few iterates (which is also what guards against late drift). Mentions the Convergence Tolerance control.

Convergence panel tabs (01-basics.ts step 7, 04-interpreting.ts step 2)
Both described tabs that no longer exist ("Threshold", "Spike Eff."). Rewrote them against the real ConvergencePanel tabs — Asymptote / Kernel / Distributions:

• Basics leads with the Asymptote dashboard (the four signals that should flatten: kernel shape, kernel-fit R², PVE, activity stability).
• Interpreting uses Asymptote as the first health check and notes the convergence marker; per-cell alpha/PVE/event-rate now correctly attributed to the Distributions tab.

Kernel quality (04-interpreting.ts step 3)
Documents the new degenerate-fit warning (⚠ n/N fits degenerate, from the #162 FitMode work) as a cue to raise coverage or re-tile.

Theory figures (theory-figures.ts)
Now draw with the shared colorblind-safe Okabe-Ito palette imported from @calab/ui/chart (spikes → bluish-green, cutoff → orange, kernel → reddish-purple, dropped → neutral grey) instead of the old D3 category10 green/orange — making the "match the dashboard palette" comment actually true.

Verification

• tsc -b apps/cadecon clean (confirms the new @calab/ui/chart import resolves).
• eslint + prettier clean.
• Static-only; I did not spin up the browser for this one — happy to Playwright-verify the theory figure render on request.

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