fix(docs-sync): raise output token cap to 16384 for Sonnet 5.5

[soheimam]

Why

#2068 switched the docs sync to Sonnet 5.5. On the first real run (run 37331981837), the re-sync of base-std@3820cf0 dropped a page: seize-and-cancel-units.mdx (8,955 chars) hit the 4096-token output cap (stop_reason=max_tokens), and the truncation guard rejected it. That's why #2069 touches 8 files where #2054 touched 10. introduction.mdx used 4,093 of 4,096 tokens, so it nearly failed too.

Sonnet 5.5's tokenizer uses more tokens per char than 4.6, so the old 4096 budget (measured on 4.6 at 10.7k–14k chars) no longer fits pages the route table sends to the model.

Changes

• llm/client.mjs: DEFAULT_MAX_TOKENS goes from 4096 to 16384. CLAUDE_MAX_TOKENS still overrides it.
• release-utils.mjs: MAX_REGENERABLE_CHARS goes from 10000 to 32000 to match. This is the pre-call skip for pages too large to regenerate (~2.2 chars/token measured on Sonnet 5.5, with margin).
• index.mjs: doc comment updated.

The truncation guard is unchanged. If a page still overflows, it is rejected rather than committed partially.

Cost and risk

• Output is billed per generated token, not per cap. Short pages cost the same.
• Calls are streamed, so a longer generation doesn't hit the gateway's ~90s buffered timeout.
• I confirmed that the gateway accepts max_tokens: 16384 for claude-sonnet-5-5.
• No workflow, permission, or secret changes.

Tests

npm --prefix scripts run test:base-std-sync: 166 pass, 1 fail. The failure (upstream docs tree routes to the pages the IA guidelines assign, an extra events.mdx route) also fails on master before this change and is unrelated.

Follow-up (separate PR)

Re-running a sync briefly resets its branch to master, which makes GitHub auto-close the open PR (that's how #2054 was closed and replaced by #2069). The fix is to commit on a temporary ref and move the PR branch in one step.

[cb-heimdall]

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