docs: enrich Actor development pages from help-center articles

[marcel-rbro]

Salvages still-useful content from four retiring help-center articles into the platform docs, so the information survives the help-center wind-down and lives in one place.

• Continuous integration: replaces the outbound "Bitbucket CI guide" link with an in-page Bitbucket Pipelines section (modernized YAML on node:22, secured APIFY_TOKEN, tests before push, branch-based build tags).
• Usage and resources: adds reference compute-unit rates and a test-run method for estimating consumption, and repoints the two former help-center links in-page.
• Builds: adds a versioning best-practices subsection for public Actors.
• Monetize: adds a section on compensating users for failed runs with platform credits.

Part of the help-center audit; a companion PR covers the Integrations articles.

[apify-service-account]

✅ Preview for this PR (commit e32f633d) is ready at https://pr-2826.preview.docs.apify.com (see action run).

[tomnosek]

I think the content team said that using "credits" is a no-no, and that we should use "prepaid usage". Verify.

[tomnosek]

If you're contacting support as a user
This feels a bit awkward - aren't they all users? How do you distinguish them?
Technically, it works based on whether they currently have any public Actor in Store.

[tomnosek]

I do think that this section is quite simplified and the "How to talk about compensation" section in Help Center is more descriptive for the publisher. Since they'll be scanning this info, chances are that they'll skip these three bullet points altogether. Since we've had quite a lot of problems with this, it deserves much bigger space and attention.

[tomnosek]

I've left a couple of comments (not a proper review though, just a random stumble), but my overall impression is that it expands a subpar page, creating even more subpar page 😄 The page is sort of like an incoherent reference jumping from topic to topic.

A couple of points:

• It's in the Actors > Running Actors section, so the target audience is also common users. Yet it starts by saying Actors run in Docker containers. How is that important to this topic?
• After the leading paragraph, we get the heading "Resources"... in an article already named "Usage and resources". I don't even know what you mean by it, and I've already read it twice as headings in 5 rows.
• It says about the memory that "It must be a power of 2." but it was recently changed to a drop-down menu, so it's not an important info anymore (and for dynamic memory, it's written in the dynamic memory page).
• In the middle, there's a section about Crawlee... If I'm a user, I'm like "What the F is Crawlee?" There could be a callout, but it's quite irrelevant for the broad audience, so it shouldn't be part of the main content.
• The "What is a compute unit" is in the middle, yet half of the page above talks about "CUs" and often doesn't even reference this part.
• The "What determines consumption" section suddenly talks about Playwright and Cheerio. Again, as a user, I'm completely confused.

This page jumps from topic to topic, talks about terms that I don't understand as a reader, and in the end, I feel like I haven't learned anything. With a certain level of skimming, I certainly can't configure the Run options part properly. So, I think the page should be just completely rewritten.

(Btw. I know that this commit is not adding the whole page and that it was created in the past likely in many iterations, but let's end up with a better page, not just mixing more confusion in this confusion pot.)