feat(keboola-cli): add DuckDB transformation skill

[MonikaFeigler]

Summary

Adds a new duckdb-transformation skill to the keboola-cli plugin, providing AI agents with comprehensive knowledge for writing, optimizing, and migrating DuckDB transformations in Keboola.

The skill (plugins/keboola-cli/skills/duckdb-transformation/SKILL.md) covers:

• Configuration structure and component ID (keboola.duckdb-transformation)
• Block-based orchestration and parallel execution model
• Dynamic backends (XSmall through Large), Parquet format, data type inference
• SQL writing rules: semicolons, case sensitivity, type casting patterns, DuckDB extensions
• Snowflake → DuckDB migration: data type mapping, function differences, case sensitivity changes, QUALIFY rewriting, temp table behavior
• Transformation Migration Component (keboola.app-transformation-migration) usage and limitations
• Real-world CRM (HubSpot-like) example demonstrating TRY_CAST/NULLIF patterns
• Best practices and DuckDB vs Snowflake decision guidance

Also bumps keboola-cli plugin version 1.0.0 → 1.1.0 and updates READMEs per CLAUDE.md instructions.

Related: content is aligned with connection-docs PR #916 which adds the user-facing DuckDB documentation.

Review & Testing Checklist for Human

• Verify technical accuracy of case sensitivity claims — the skill states "column names are always case-sensitive regardless of quoting." This comes from the component README, not standard DuckDB docs. Confirm this matches actual runtime behavior in Keboola.
• Review the ~85% / ~25% migration estimates — the skill states SQLGlot converts ~85% of Snowflake SQL and ~25% of migrations need manual fixes. These are user-provided estimates. Consider whether AI agents should present these as hard numbers or soften the language.
• Check HubSpot CRM example appropriateness — the real-world example uses HubSpot-like field names (companyId, hs_analytics_source, etc.) in a public repo. Confirm this is acceptable or if it should be made more generic.

Suggested test: Install the plugin locally and ask Claude Code a few DuckDB transformation questions (e.g., "how do I migrate a Snowflake QUALIFY query to DuckDB?", "what backend size should I use for a 7GB dataset?") to verify the skill triggers correctly and produces accurate guidance.

Notes

• This is a knowledge-only change (no executable code). CI can validate JSON syntax but not content accuracy.
• The SKILL.md frontmatter follows the same pattern as the existing keboola-config skill.

Link to Devin session: https://app.devin.ai/sessions/ae19dd2027b64ddc87769f9a9dd7538e
Requested by: @MonikaFeigler

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