feat(query): add --database flag and improve post-load UX

[eddietejeda]

Summary

• Adds `--database` / `-d` flag to `hotdata query` so a managed database can be scoped per-query without running `databases set` first
• Adds `ApiClient::with_database()` builder method to override the `X-Database-Id` header for a single request without touching config
• After `databases create` (table output), prints a ready-to-run example with the correct `databases load` dot-notation syntax, the `--database ` flag, and the `default..` SQL prefix
• After `databases load`, prints a ready-to-run `hotdata query` command and a tip that uppercase column names require double-quoting

Test plan

• `hotdata query --database <db_id> "SELECT * FROM default.public.
LIMIT 10"` works without `databases set`
• `--database` overrides a previously set current database
• `hotdata databases create` table output shows correct `databases load` and `query --database` examples
• `hotdata databases load` output shows correct `hotdata query` example with case-sensitivity tip
• All existing unit tests pass (`cargo test`) — 165 pass; 3 pre-existing config env failures unrelated to this PR

🤖 Generated with Claude Code

[sentry]

Codecov Report

❌ Patch coverage is 0% with 32 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/query.rs	0.00%	11 Missing ⚠️
src/databases.rs	0.00%	9 Missing ⚠️
src/main.rs	0.00%	8 Missing ⚠️
src/api.rs	0.00%	4 Missing ⚠️

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