Enhance documentation with detailed examples

- tiers.md: Complete rewrite with examples for all four tiers
  (Lookup, Manual, Imported, Computed), auto-population, choosing
  the right tier, backup considerations
- dependencies.md: Comprehensive foreign key documentation with
  examples for primary/secondary FKs, options (nullable, unique),
  renames, dependency patterns (hub, chain, fork/join)
- insert.md: Detailed insert operations with dict/list/DataFrame
  formats, all options (skip_duplicates, ignore_extra_fields,
  replace), batch inserts, server-side inserts, object attributes
- fetch.md: Complete fetch reference with output formats, sorting,
  limiting, blob handling, object attributes, performance tips
- restrict.md: Thorough restriction guide with all condition types
  (dict, string, table, query), combining conditions, practical
  patterns, performance tips, common mistakes

Author: claude