fix: Fact-check of database docs

[Swiftaxe]

Summary

Fact-checked, removed noise, and added frontmatter to all 20 database pages.

All 20 files:

• Added missing description frontmatter

Code bugs fixed:

• 02-models: // comment in YAML block → # (invalid YAML syntax)
• 06-filter: first equals example was missing session argument
• 08-sort: prose described a non-existent orderDecending: true parameter → corrected to .desc() (also misspelled)

Grammar & typos:

• 01-one-to-one: "both sided" → "both sides"
• 02-one-to-many: missing verb "the name parameter with a unique string" → "takes a unique string"
• 04-self-relations: "relation ship" → "relationship"
• 07-relation-queries: "return a employee" → "returns an employee"
• 02-models: "as have always been" → "by default"
• 14-client-side-database: "to use it all database operations" → "to use it for all" (in code comment)

Noise removed:

• 05-crud: version history :::info about previous insert mutation behavior (Fix the path of the docker directory #12)
• 05-crud: :::note exposing ON CONFLICT DO NOTHING SQL internals — replaced with prose keeping the useful constraint behavior info
• 05-crud: "At least one column must be specified…otherwise an ArgumentError" (Getting started #14)
• 08-transactions: "At the time of writing" from isolation level :::info
• 01-connection: two redundant lead-in sentences
• 03-referential-actions: onUpdate/onDelete wrapped in backticks; added missing period

Formatting:

• 10-raw-access: removed extra indentation from two code blocks
• 08-transactions / 13-row-locking: fixed MD060 table column style lint errors