docs: comprehensive review across all user-facing documentation

[bigin]

Audits 18 files: README, CHANGELOG, every tutorial chapter, every API reference page, the field-types and query cookbooks, the deployment guide, and the 1.x to 2.0 migration guide.

Content corrections (each verified against source):

• storage.md: generated-column SQL example now gen_<catId>_<field>
  • VIRTUAL (was field_<name> + STORED); migration table updated to .sql extensions and to include 0005_searchable_defaults.
• api/field-types.md: InputErrorCode::PatternMismatch in the custom-plugin sketch replaced with WrongValueFormat (the invented case was supposed to have been removed in 2.0.0). defaultConfig() table rewritten against the actual plugin sources: all 16 built-ins now listed with their real keys and defaults. New callout explains the documented divergence between fluent-setter keys (maxBytes, mimes, format) and the upload plugins' runtime keys (maxSizeBytes, acceptedExtensions).
• domain.md: config examples switched to plugin-read keys (maxLength, acceptedExtensions) instead of stale max / mimes.
• tutorial/files.md: FileStorage is a seven-method interface (text incorrectly said five); thumbnail code-block typo $thumbThumbPath resolved by inlining $thumbRelative.
• query-cookbook.md: EXPLAIN QUERY PLAN example now uses gen_7_active (matching the actual generated-column naming); migration-format link bumped to 0001-0005.
• migration-guide.md: composer constraint bumped from the stale 2.0.x-dev to ^2.0; --database flag corrected to --db; schema-status output and prose reflect five migrations (was four).
• README + tutorial/README + tutorial/setup + api/README + cookbook: version reference bumped from 2.0 / 2.0.2 to 2.2.1 (or "iManager 2" where the line is what matters); README CLI table optimize row clarified (--vacuum is opt-in, not always run).

Independence cleanup (the project rule that iManager docs never name their consumers had drifted in a few places):

• CHANGELOG 2.2.0/2.2.1: removed downstream-consumer naming and the specific schema field list.
• tutorial/setup.md: removed the "Scriptor's frontend" example for the cache path.
• tutorial/schema.md: removed the Scriptor-specific perf-smoke paragraph and swapped "scriptor" as an example search term for "introduction".
• tutorial/search.md: removed the same Scriptor perf-smoke paragraph (left "scriptor" as an example search term per request).

Style pass: roughly 250 em-dashes used as connectors replaced with periods, colons, commas, or rewritten sentences across the corpus. Heading-style em-dashes (## Step 1 - ...), Keep-a-Changelog version headers (## [2.2.1] - 2026-05-17), legitimate two-dash parenthetical pairs, and verbatim CLI output are preserved.

No code changes; no public API changes.