docs: add Java SDK documentation

[MarketDataDev03]

docs: add Java SDK documentation

Adds the documentation for the Java SDK under sdk/java/, following the same
structure and format as the existing SDK docs (Docusaurus MDX with <Tabs>). It
also adds Java and Kotlin code examples to the existing api/ reference pages,
alongside the other languages.

• Base: MarketDataApp/documentation → staging
• Head: MarketDataDev03:01_sdk_java_docs

What's included

sdk/java/ — the documentation (25 pages)

• Getting started: index, installation, authentication, client, settings
• Resources: stocks (candles, quotes, prices, news, earnings), options
  (lookup, expirations, strikes, quotes, chain), funds (candles), markets
  (status), utilities (status, user, headers)
• Every quick-start has both a Java and a Kotlin example (first-class Kotlin
  interop is a requirement of the SDK).
• All method signatures, request builders, response records, enums and exception
  types were verified against the SDK source — the snippets compile.

api/ — Java & Kotlin examples on every endpoint

Adds a Java tab and a Kotlin tab to every language-tab group in api/*
(alongside HTTP/JavaScript/TypeScript/Python/Go/PHP), so the REST reference shows
JVM examples too. 22 tab groups across 19 pages — coverage is complete
(Python = Java = Kotlin = 22).

• Endpoint pages use the real SDK, mirroring the existing JavaScript example in
  each group (same symbols/variants).
• api/stocks/bulkcandles: the SDK has no bulk-candles method yet, so the Java
  and Kotlin tabs use the JDK java.net.http.HttpClient directly with a :::note
  (same approach as the JS/TS/Python tabs there).
• Troubleshooting pages (logging, real-time-data, service-outages,
  too-many-concurrent-requests) get tailored Java/Kotlin equivalents using the SDK's
  real features (logging via MARKETDATA_LOGGING_LEVEL, ServiceStatus,
  RateLimitError backoff, Mode.LIVE + StockQuote.updated()).

Shared files (flagging for review)

These touch site-wide files, not just sdk/java/:

• sdk/index.mdx — adds the Java card to the SDK landing page.
• static/img/java-logo.svg — the Java logo for that card.
• docusaurus.config.js — adds java, kotlin, groovy to Prism
  additionalLanguages so the code blocks get syntax highlighting.

Docs → SDK sync (Phase 2)

Enables the existing sync pipeline for Java:

• scripts/export-sdk-docs.js — adds java to SUPPORTED_SDKS.
• .github/workflows/sync-sdk-docs.yml — adds java to the trigger paths, the
  workflow_dispatch options, and the job matrix.

Testing

• yarn build passes with no broken links/anchors.
• api/ tab coverage verified: every group that has a Python tab now has a Java and
  a Kotlin tab (22 / 22 / 22).
• node scripts/export-sdk-docs.js --sdk java converts all 25 sdk/java .mdx →
  clean .md + .sync-manifest.txt (Tabs → headings, no leftover JSX), exit 0.

Follow-up (NOT in this PR — needs org admin)

For the sync to actually publish to MarketDataApp/sdk-java, the
marketdata-docs-sync GitHub App must be granted access to the sdk-java repo
(Contents: R/W, Pull requests: R/W). Once granted, the first push to
staging touching sdk/java/** opens an automated PR in sdk-java.

Checklist

• Base branch is staging (not main)
• Preview verified on www-staging.marketdata.app/docs/sdk/java/ after merge
• GitHub App granted access to sdk-java (separate, org admin)
• Maven version in installation.mdx matches the published release

[MarketDataApp]

Guiding principle for the API-section SDK examples: optimize for "look how easy this is."

A reader skimming the API docs should see they can get data from us in 1–3 lines. The Java/Kotlin examples should read as minimally as the JS/Python ones next to them. Two concrete rules:

1. Use the convenience factory, not the builder, unless the example is about an optional param.

// instead of
StockCandlesRequest.builder(StockResolution.DAILY, "AAPL").build()
// use
StockCandlesRequest.of(StockResolution.DAILY, "AAPL")

Keep the builder only where the optional parameter is the point of the example (e.g. markets/status demonstrating .from(...).to(...)).

2. Let the records print themselves. Every response row is a Java record with a generated toString(). Replace field-by-field printf loops with:

candles.values().forEach(System.out::println);

Blocked on the SDK: the multi-symbol examples (stocks/quotes, troubleshooting/logging) use StockQuotesRequest.builder(...) because that type has no of(...) factory — every sibling request type has one. Tracked in MarketDataApp/sdk-java#17. Once that ships, these examples can go minimal too; until then they stay on the builder.

Net effect — the canonical single-quote example should look like this and nothing more:

try (MarketDataClient client = new MarketDataClient()) {
    client.stocks().quote(StockQuoteRequest.of("AAPL")).values().forEach(System.out::println);
}

[MarketDataDev03]

Guiding principle for the API-section SDK examples: optimize for "look how easy this is."

A reader skimming the API docs should see they can get data from us in 1–3 lines. The Java/Kotlin examples should read as minimally as the JS/Python ones next to them. Two concrete rules:

1. Use the convenience factory, not the builder, unless the example is about an optional param.

// instead of
StockCandlesRequest.builder(StockResolution.DAILY, "AAPL").build()
// use
StockCandlesRequest.of(StockResolution.DAILY, "AAPL")

Keep the builder only where the optional parameter is the point of the example (e.g. markets/status demonstrating .from(...).to(...)).

2. Let the records print themselves. Every response row is a Java record with a generated toString(). Replace field-by-field printf loops with:

candles.values().forEach(System.out::println);

Blocked on the SDK: the multi-symbol examples (stocks/quotes, troubleshooting/logging) use StockQuotesRequest.builder(...) because that type has no of(...) factory — every sibling request type has one. Tracked in MarketDataApp/sdk-java#17. Once that ships, these examples can go minimal too; until then they stay on the builder.

Net effect — the canonical single-quote example should look like this and nothing more:

try (MarketDataClient client = new MarketDataClient()) {
    client.stocks().quote(StockQuoteRequest.of("AAPL")).values().forEach(System.out::println);
}

Thanks, makes sense — applied both rules across the api/ examples: switched to the .of(...) factory (keeping the builder only where an optional param is the point), and let the records print themselves via ....values().forEach(System.out::println).

For the blocked multi-symbol case, opened MarketDataApp/sdk-java#18 (closes #17), which adds the of(...) factory — those examples now use the minimal form too.