docs(duckdb): correct connector memory/spill guidance (no connection-string channel)

[claudespice]

Summary

The DuckDB data connector deployment guide told users, in the Capacity & Sizing section, to configure DuckDB via a channel the connector does not expose:

• Memory: "set a memory_limit pragma via the connection string"
• Temporary spill: "set temp_directory to a fast local volume"

Neither is actionable. The DuckDB connector exposes exactly one parameter — duckdb_open (a file path or :memory:) — and opens the database read-only. There is no connection-string input, no memory_limit parameter, and no temp_directory/pragma channel. This is the same fabricated-mechanism class as the DuckDB/SQLite accelerator guides fixed in #1906; the connector guide was the latent second occurrence.

This corrects both bullets to describe DuckDB's actual (self-managed, internal) behavior and points readers to the DuckDB accelerator, which really does expose a configurable duckdb_memory_limit acceleration parameter, when they need a Spice-configurable limit.

Verified against code (spiceai/spiceai)

• Connector params — only open, opened read-only: crates/data-connectors/connector-duckdb/src/lib.rs:162 (const PARAMETERS: &[ParameterSpec] = &[ParameterSpec::component("open")...]); no connection-string / pragma parsing.
• Confirmed identical at the release tags backing the versioned docs: open-only at v2.1.0 and v2.0.1.
• Accelerator duckdb_memory_limit exists (crates/runtime/src/dataaccelerator/duckdb.rs:418, ParameterSpec::component("memory_limit")) — present at v2.1.0 too — so the cross-reference is accurate.

The identical wrong text lived in vNext + version-2.1.x + version-2.0.x (correction predates versioning), so all three are fixed here.

Test plan

• cd website && npm run build passes (Docusaurus onBrokenLinks: 'throw'; the added ../../data-accelerators/duckdb link resolves — same path already used in the page's Known Limitations section, target confirmed present in each versioned tree)
• Versioned-docs propagation checked — grep for "pragma via the connection string" now returns zero hits across connector pages in all versions
• Files updated: 3 (vNext + 2.1.x + 2.0.x connector deployment guides)

[github-actions]

✅ Pull with Spice Passed

Passing checks:

• ✅ Title meets minimum length requirement (10 characters)
• ✅ Has at least one of the required labels: area/blog, area/docs, area/cookbook, dependencies
• ✅ No banned labels detected
• ✅ Has at least one assignee: claudespice

[github-actions]

🚀 deployed to https://28831e61.spiceai-org-website.pages.dev